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MG MGB Technical - Electrical Guru needed starting issues continue

fuel pumptrying to trouble shoot my starting issues. Need an Electric Guru. It

GG Ginty

All relays work same way, you have primary connection field where you can find +12 V from ignition switch (referring to MGB workshop manual is blade marked with W1, but on modern relays are numbers 30 and 87 is primary side, 85 and 86 secondary side) and second blade W2 from primary side is grounded. When is current flowing relay engage secondary circle. One wire from secondary circle (blade C1) comes from unfused power supply (brown color) and goes via C2 to starter motor, to be more precise to starter solenoid (with one fat cable that comes directly from battery).
Looking to your picture I am guessing that is thin yellow/red one that comes from ignition switch, red one (thicker) is most probably unfused +12 and thick black should go to starter solenoid (or vice versa). What I can not se is ground connection on primary side. Find short wire and connect third pin to good ground, you can use screw that hold relay to car body.
If you assume that is relay out of order make simple bridge between both thick wires (red and black), that should turn on starter motor.
If that does not help then you have to go further and check grounding of starter motor and after that starter solenoid (part of starter motor) but usually it does not give up so easily so I would say that is problem good ground. You have to know that is starter motor the biggest current eater in the car so if you do not have good earth from engine to car body it will not get enough amps and will not be able to turn around the engine.

Toni Kavcic


I am pretty sure that the relay is good from my testing but the relay never had a ground and the empty terminal never had a ground in the six years I have had the car.

Does it need a ground the wiring schematics shows a grounding, but mine never had one
GG Ginty

You are not demonstrating a relay, you are demonstrating a Ford starter solenoid. Your 74 should have the Lucas pre-engaged starter which has its own solenoid. Thus, you have introduced a second solenoid into the system rather than a starter relay and a solenoid on the starter motor itself as the factory designed the system to operate. Will this have some effect on the system? I do not know. But, it is a variable which may have to be considered.

The use of two solenoids can also cause some confusion when we discuss what issues might be present. For instance, you note that the battery voltage (presumably not under load) is 12.8 volts and the hot (brown) wire reads an erratic 12.5 volts on the "starter relay" (presumably the Ford solenoid). They should read the same and the reading off the brown wire circuit, in toto, should read battery voltage if all of the connections are clean and securely made. Voltage drop, especially when not under load, indicates a problem which, under load, can lead to significantly reduced voltages within the system.

The first thing to check, since your starter relay has been replaced with the Ford solenoid, is whether you have the factory style starter, with its attached solenoid, installed on your car. One of the reasons to replace the factory starter relay with a starter solenoid would be because a different style of starter (one without an attached solenoid) has been installed.

We need to know what starter you have.

Second thing to test is the voltage of the battery under load. Hook up a couple of jumper wires, having large clips on one end (battery terminal end) and smaller clips to attach to the probes of your volt meter. Turn the ignition switch to the start position and note the battery voltage reading. If it drops a full volt, the battery terminals and the cable clamps need to be cleaned and retightened. Do the test again and, if you still note the voltage drop, have an assistant hold the probe ends to the battery terminals themselves as you test again. A drop at the terminals indicates a possible bad battery. No drop at the terminals, with a drop at the battery cable clamps indicates a problem with the clamps.

If all is good at the battery end, take your jumper wires and attach the one which was on the positive terminal of the battery to the main terminal of the starter, the one where the brown wires and the cable from the battery attach. Hook up your volt meter to this wire and hook the negative jumper wire to a good ground. Turn the ignition switch to the start position and note the battery voltage at the main terminal of the starter. If the cable from the battery to the starter is bad (or the connections are not tight on the starter) it is common to see a significant drop in voltage. About four volts were read on the two vehicles I had to test in this manner. If you get a reading of less than 11.5 volts, the cable between the starter and battery need to be replaced before further testing can be done.

If you can supply the information I have requested, we will be in a much better position to assist you in your trouble shooting.

Les Bengtson

It sounds like a classic lack of current. I would like to hear what happens with another battery.

As a matter of routine, these cars need a second ground - most of the old hands earth the engine to the chassis where they can eyeball it easily.

R Walker


I have had the car six years and it came with that ford starter relay/solenoid (or whatever it is ) along with a stock Lucas starter motor. At the time I did not know it was a ford starter relay/solenoid (or whatever it is ). The car ran great for three years with the ford “whatever it is” and a stock Lucas starter. So if my logic is correct, my setup with the ford “whatever it is” and stock starter motor is fine.

The original starter died (or so I thought) in May 2009 and I replaced it with a stock Lucas starter from my 77 parts car. Car started up fine and ran great for a few months and then became sluggish to start and finally a clonk while out driving. Got a push start and drove it home. The following morning, clonk. Did some testing and fiddling around without any luck. I got another stock Lucas starter from a dealer at the British Invasion in Stowe VT in September 2009 and replaced the “bad” one with this. Started up fine, ran great for a little while and “died” in November 2009.

The current starter is a stock Lucas starter I got from Moss in November 2009. When I installed it and went to start up all I got was the clonk, fiddled around and eventually it fired up and I drove it for a few weeks without a problem until December 2009 when starting up became sluggish. One morning, clonk, did some testing over a few days with no luck, so I put it away for the winter. In March 2010 I decided for the hell of it see if the car would turn over. The car fired up first time! I drove it around from March without any problems starting until the Fall time when starting up became sluggish. Also I started to have issues with the alternator, so I replaced the alternator along with a new battery. Car fired up straight away and I drove it around town that day with no issues. The following morning clonk and that’s where it has been since.

The posts on the battery are fine, clean and tight. Both grounds are fine, clean and tight. I have been told that the ford starter relay/solenoid (or whatever it is ) should be ok and like I said that’s how my 74 came. All I know is that some PO decided for whatever reason decided to replace the stock starter relay with the ford starter relay/solenoid (or whatever it is ) and use none stock wiring and splice into the stock wiring harness.

The testing I did was to rule out a faulty ford starter relay/solenoid (or whatever it is ) and determine what goes to what since the wiring is none stock. I did unwrap some of the taping up which you can see in the photo and I now know what is spliced into what and correcting this is another issue

I feel as though I am chasing some ghost here. As I said I am not very mechanically/electrically minded.

GG Ginty


Maybe I need to go back and read ALL of the ("long winded") information and detail that you provided before I throw a couple cents into the ring but, hey!! Just trying to help, to some extent.

Les noted that you are working on a 1974. It looks like the under bonnett of a MGB and based on single carbon canister and 4 fuse fuse block, I would guess that your car is of the ~1974 timeframe with, as Les noted, the starter solenoid as part of the starter. Would like to see a photo of the starter is at all possible. Earlier MGB's, and midgets, did not have starter solenoids on the starter. They had a seperate starter solenoid/relay/whatever it is on the inner fender similar to what you have here. More interesting(!?!?!) assuming some of your trouble shooting has been associated with "whatever this is", I am not sure that it is in your starter circuit!! If this "what ever it is" is in your starter circuit I am REALLY confused as to why none of the 3 wires shown (heavy gauge red, brown with yellow stripe, and purple(?)) are heading south towards the starter. Thare are all heading north into you wire harness and then to . . . . . ??? Unless you REALLY know this is in the starter circuit, you may want to ignore it for now and concentrate on voltage to your starter at the starter. You might also, as noted by someone else, take a jupmer cable and connect to the engine somewhere and then to the frame to make sure you have a good ground.

Along the line of the battery/batteries, do you have 2, 6 volt or 1, 12 volt. Assuming you, or previous owner switched over to single 12 volt, how is the battery grounded to the body? HOPEFULLY someone put a new ground cable from the single 12 volt directly to the hole in the battery box/bracket. Check to see that you have a GOOD clean earth ground at the battery. I usually use SS star washers that bite the metal to make sure that you have a good earth ground.

Well, although a little long winded and more than you were looking for, I hope that helps. Would be curious to hear your response to some of the questions and comments made above.

Again, HTH.

Fred Wright

You said, "Checked the voltage on the “hot” wire at the starter relay and it reads about 12.5, though it fluctuates a lot, not steady like at the battery. This might be because I am not finding a decent ground on the engine with the tester."

It shouldn't be that hard to find a good ground on the engine, so do that test again. It may be that your crimp-on connectors are poor.

The Ford relay/solenoid is commonly used as an aftermarket solution. I have used them in several applications, and never used the extra terminal for anything. Once I knew what it was for, but don't remember now. However, it is not a ground. The unit grounds by bolting it on to the car, so remove it and clean up the mounting.

Trace your wiring and clean up ALL the connections associated with the starting circuit.

What was the failure mode of all the starters you have put on it?

C R Huff


Thanks.. Yes I use the term "whatever it is" in a bit of tong and cheek joke. I am sure that it is part of my starter circuit because if I disconnect the center wire (yellow) and go to crank the ignition I only get the ignition light and the clicking of the fuel pump. Connect back up, crank and I get the usual followed by a very faint click and then the loud clonk.

I am sure the wiring is correct as I unwrapped the electrical tape mess where the three wire from "whatever it is" disappears into. The big red one goes to brown, yellow to what looks like red/white and the black one to brown and white.

I'll assure you it is the correct starter motor with the starter solenoid(Moss 131-220), just like the other three I have replaced and now sitting on my garage floor. The car is an October 73 build.

I have put a fresh positive battery clamp on the battery cable and polished the terminals until they shine. I converted to a single 12V two years ago and the I installed a new negative ground for it then. The ground is good and tight and nice bright metal where is attaches to the body

I have removed the main ground and checked, no corrosion etc and is now tight.

When someone says to "turn the ignition key to the start position".. do they mean just to turn key the until the ignition light comes on, or do they mean to crank the engine to get it to turn over?. If I turn the ignition key until the light comes on and not crank I do not get any readings on the other two posts on that ford relay/solenoid(or whatever it is). Shouldn’t I get some form of reading?

I know this is a stupid silly question, but just trying to get a better feel as to how things work and not have to ask such daft questions!.

Once I can figure all this out I aim to put a little bit more sense and intelligence into the wiring and return it back to some level of normality. Even the wiring at the alternator is not stock as I found out when I replaced the alternator last year.

I thank you for all your patience
GG Ginty

"Turn the ignition switch to the 'start' position" means to turn the switch, against spring pressure, to the position which energizes the starter motor circuit. When the key is returned, by the spring pressure of the switch, it defaults to the "run" position which provides power to the white wire circuit which provides power to the low tension ignition circuit and fuel pump, but not to the starter relay and, through the starter relay, to the starter solenoid.

Again, what is the voltage reading, at the main starter terminal, when the ignition switch is in the start position? If it is not in the 12v range, there is a problem between the battery and the starter motor. If there is at least 12v when cranking/trying to crank, the problem is elsewhere.

I am assuming that the "new" starters are rebuilt units. I have seen some of these test bad out of the box. The quality of rebuilds is quite variable and it is perfectly possible to have one, or more, bad starters as delivered by the various parts retailers.

If you have full battery power, at the starter terminal, and the battery voltage does not drop with the ignition switch in the start position, you are not supplying power to the starter solenoid or the solenoid is not operating the starter. Once again, this is a quite basic test, the results of which are necessary if we are to assist you.

Les Bengtson


SORRY(!!!!!!) to say that I threw you a bit of a curve ball!!!!! BUT, with some of the additional information that you have provided, maybe a suggestion. First, let me do some cleaning up (after myself).

Your 1974 MGB had a square metal can Lucas relay near the fuse box at one time. The wires on the relay, as you may have suspected, were the ones that you found connected to the wires going to your “whatever it is” FOMOCO device. The red one, going to brown should ALWAYS have a ~12 volt reading. I believe it is safe to say that ALL brown wires on an MGB harness are ALWAYS 12 volts. These brown wire are unfused and basically coming from your battery via a connection on your starter. The black(ish) wire on the other lug should be going down to your starter and should NOT have 12 volts on it unless you are in the “Start” (not run/on) position of your ignition switch (against the spring pressure). The other wire, which I believe is actually white with a red tracer is coming from your ignition switch. This is the yellow wire on your “whatever it is”.

Okay, I believe Toni basically provided the same suggestion but let’s try it another way. You need a small piece of jumper wire. FIRST, make sure the car is in neutral and wheels are chucked or you have E brake on!!! Put your key in the "on" position. Not start (against spring pressure). This is the same position your key would be in if you were driving down the street after starting the car. Now, from under the bonnet, verify that you have ~12 volts on the red wire and 0 volts on the black wire. Assuming you have the 12 and 0 as I suggested, take the small jumper wire and jump between the red wire and yellow wire. This should engage your starter relay . . ooops. You should now see 12 volts on the black wire and hopefully your starter is turning. Your car may even start!!!. If you do not see 12 volts on your black wire, there is something wrong with this relay thingie. Possible a ground to chassis with the bolts going through the inner fender or just an internal problem and time to replace it. As it may be easier, and cheaper, at this time, to just replace this relay/solenoid/whatever it is, you can probably get one from the local auto store. They are common and used in lots of applications. The last thing you might want to do is go directly from the red wire to the black wire. You may want to use a little heavier piece of jumper wire for this test otherwise the wire is going to get hot real quick. By jumping across this device, you are basically eliminating the start position on your ignition switch.

Again, HTH and again, SORRY for throwing you a curve ball in previous response.


Ps, Your car does not too badly altered relative to the wiring under the hood in this area. Appears that all that PO did was replace Lucas relay with aftermarket unit that is more readily available. Connections on fuse block have been replaced but nothing new about that. The only problem you may have is with old fuse/dirty fuse connections and any crimp on connectors on white (ignition) and brown (12 volt) wires. Make sure that they are all good and tight!!! If you can, replace crimp connections with solder on style. Still, old fuse boxes tend to provide loose and intermittent connections. Not to expensive to replace!!!
Fred Wright

GG, I've had a quick look at the North American (NA) wiring diagram and there is an additional starter relay which is not fitted to cars for other markets. This relay will have a brown (shown as N in a wiring diragram), brown and white (NW) and (this is where yours is different) a yellow and pink (YK). The brown should be permanent 12v, the brown and white is the other side of the relay contacts and is connected to 12v when the ign sw is turned to "crank" (we call this start in the UK!).

Now to make this happen the YK needs to have 12v on it when the ign sw is at crank and it needs an earth which we'll assume is via the metal body. So the first thing to check is you have 12v on your yellow wire at the relay when you sw to crank? If not you need to confirm if you have seat belt warning/inhibitor system fitted or find out where your yellow wire comes from. If yes, next check if you have 12v on the NW (your black). If no the relay is US (UnServiceable!), if yes we move on to the starter....
The starter will have the main feed from the battery and number of N wires connected to some spade connectors. Assuming the main feed is tight we'll not worry about the others for now.. There should also be a NW wire which runs down from your starter relay. check this has 12v on when in the crank position. If NO the cable between the relay and starter is US. If yes, the starter solenoid is suspect. The easiest way to rule this out is to replace the starter motor but as you've done this a few times we can deploy a few tricks... Get a big screw driver and short the two big terminals on the end of the solenoid and the motor should run and turn the engine over. No need to hold it for long as you'll know straight away if it does!!!! It might be a bit difficult to get a screw driver in there and one jump lead cable might be easier...

If all this seems too much just take it one step at a time and we'll help you along.

M McAndrew

Fred, guess we were typing at the same time......

Do you know anything about the seat belt interlock shown in the Haynes rag for this model year?

M McAndrew

voltmeterems to me we've been here before, but...

Key switch has 4 possible positions
OFF (only position where key will come out)
ACCESSORY (usually radio only)
IGNITION (Ignition, fuel pump, instruments, other things only need when car is running)
START (starter only, spring loaded momentary contact)
Some cars (not MG) put ACCESS before OFF, so that you don't accidentally get IGN when you want ACCESS.
Some car do not have ACCESS, putting all functions except START on IGN.

"Solenoid" is a description of an electromechanical device that produces motion. It is by definition a hollow centered coil of wire that produces a strong magnetic field in the center when current is passed through the coil. The field pulls a magnetic core (iron) in to the center of the coil. That motion is what causes the "clonk", as the core hits the end of travel.
This motion/force can be used to close a set of contacts, in which case it is a "solenoid switch" = what the Ford device you have is.
Or, the motion can be used to move a mechanical component.
The Lucas integral "solenoid" does both = two things: it first engages the starter pinion with the flywheel, and then closes a set of contacts to send current to the starter motor.

"Relay" is a functional description of a part of a circuit, also applied to the physical component that performs the function. It uses a small control current to switch a larger load current. It can be a solenoid switch (which is always functionally a relay), or the common electromechanical relay, or a solid state device.

The common electromechanical relay is similar in concept to the solenoid switch, except that the iron core is fixed in position and does not move. It does become a magnet when the coil is energized, and attracts another magnetic piece, operating a set of contacts. Since it is not moving a big chunk of iron, it is smaller, more efficient = less current draw, faster, and quieter = no "clonk" but a "click". But, since the contact forces cannot be as high as the solenoid switch, nor the travel so great, it is not as good for very high current switching. The EM relays are usually limited to about 40Amp in automotive use, while the solenoid switches are 50A and up past the 200A that a starter can pull.

OK, on to your problem.
The Ford solenoid switch is acting as the stock starter EM relay did; I suggest you replace it with the correct item. Standard Bosch type relay ($10), 4 terminals labeled 30 (Battery power = browN), 87(Starter solenoid operating = White/browN), 85
(Black = ground), 86 (control from Ign switch START = White/Red). Replacing this will probably not fix your problem, unless you happen to fix the bad wires/connections in the process, but it will lessen confusion.

"Checked the voltage on the
FR Millmore

Well, don't everybody type at once!
Mike, what wiring diagram is that ? I think I have all of them, and I don't see any Y/K wire, and I can't recall ever seeing one either.

FR Millmore

FRM, I did qualify by saying it was a Haynes diagram! It's titled "typical wiring diagram 1973/74 N American models" Item 174 starter solenoid relay. YK links to item 245 "sequential seat belt control"! Whatever that is!!


M McAndrew

Thanks everyone and a lot has been cleared in my mind over this and I have learned a lot..

Fred. I did jump between the red/black wires on the "what every it is" and I got the usual clonk. It was after that that I decided to trace the wires into the splicing and saw what I was dealing with and at this stage nothing would surprise me. In fact the brown/white wire going down to the starter has seen better days and I will be taking a closer look today.

Also I bought an OEM Lucas fuse box the other week and once I get this thing running I want to address that as well. I have issues with the fuse box on and off. Also when I replaced the alternator in December one of the connectors on the wire end literally fell to pieces when re attaching. I want to replace the entire connectors. I had a on and off problem with alternator for a while. Now I wonder if it was the wiring and not the alternator that was at fault.. I live and learn

Fletcher, Yes we have been here before and I appreciated your e-mail you sent me a month or so ago and your recent input. I just not had time this winter to get out into my cold and dark garage to do much about it

I personally think it has something to do with the brown/white wire between that whatever it is and the starter. I will keep everyone informed but most of the testing will have to wait until the weekend


GG Ginty


If you wish, send me an email to my home email address. email link provided in above responses. I will provide you my home/cell phone number and talk about what you are seeing and how to proceed, again, if you wish.

Before you run out and purchase another starter or have one rebuilt, I would suggest having your existing starter(s) tested. A local alternator or starter rebuild shop should be able to help you. So that I do not send you any bad or misleadking information I would like to review the schematic for your car and tell you how to just the wires at the starter to make sure that part of wiring is okay. Not something that you will want to do on a REGULAR basis but a means of checking other things in your circuit. I know there is a link to GREAT wiring harness informaiton for all MGs but if you are not that good at following them (the schematics) not much use in providing you with the link.

As a final note, I would not that you replace the "what ever it is" with a/the factory correct unit or any aftermarket unit until you get the real problem resolved. It does not sound like your FOMOCO device is your problem, so just leave it alone for the time being. This, assuming, as indicated above, that the connections to you FOMOCO device from your factory harness are good and tight!!!! THAT IS KEY!!!


Fred Wright

GG I think I would like to offer my two peneth into this great debate of technical information that you have been bombbarded with, and try and simplifye the problem,

1, turn your head lights on, turn your ignition key to start engine if your lights go out you have a battery problem if they stay on you have a starter motor problem,
You say you there is clonk when you turn the key as apposed to a click of a relay, this would sugest to me that the starter pinion has been pulled forward to engage the ring gear, your starter motor judging by the year should comprise of a motor with solenoid, I would sugest at this stage that the contacts in the starter solenoid are worn out and not making, this large solenoid consist of two windings one winding being the pull in winding the other the hold in winding. If the hold in winding gose open circuit you may here a lot of chattering but equally this could be a bad battery terminal which should be obivious on examining the battery, No engine earth usually results in the starter motor turning the engine over slugushly and slowly but I think your main starter motor solenoid contacts are worn or there is an obstruction stopping your pinion entering the flywheel,

Regards P,Tighe
P.T. Tighe

Thanks P.T

My aim for this weekend is to jack the car up and take a much closer look at the connections at the starter etc, see what voltage I get etc.


GG Ginty

Jacked my car up with my new 2.25 ton jack from HF with ease. I had used a smaller one before, but this time I had a much better "head room" to take a closer look this past weekend

The wiring down there MAY the root of all my previous starter problems. The brown/white wire from the starter relay has seen better days. Looks as though some of the insulation shield had worn thin somehow, not sure if it had worn through to the wire. Also one of the larger brown wires looked at first sight to be a little crusty in one spot as well. Not sure if this was due to the last time I changed oil, as I know a few drops did spill down there, or perhaps two bare wires touched somehow. Need a better light to be for sure

I have never done any electrical wiring work before and just wondering the best way to patch the mess up, to get the car on the road and perhaps address a more permanent fix (like a new harness) later. For the wires running down to the starter area (with exception of the wire from the battery), is it possible to pull them up as a whole through the engine bay and fix it up top instead from underneath the car?. Silly question!. I know that this will give me a much better view of the wiring down there and a much easier working area.


GG Ginty

First disconnect the baterry before you remove wires from starter motor Removing the earth lead will suffice. then jack car up an block with jack stands then you can remove wires safely from starter motor solenoid. I cant recall wether the tail lighting fuel gauge and fuel pump wiring are part of the harness that runs down and is part of the same harness as the starter solenoid wiring ifso then you wont be able to pull much up top. If you have sufficent length of cable at the starter motor and the terminals looked corrooded or suspect replace them.

Regards PT
P.T. Tighe

Thanks P.T

I have the car jacked up right now, and I am not too sure of the other wire runs yet, I have the schematics so I will take another look this week for a weekend fiddling around.

I have other wiring issues under the bonnet. Eventually I will be looking to replace the harness, but for the time being I just want the car running down the road. Too many people are asking if Wigan is out of the garage yet. Too embarrassed to say no..


GG Ginty

I'm also not sure if the cables are long enough to feed to the top side. It's been 20 years since I messed around down there!
But, when you work out how to get to the offending wires there's basically two ways to repair. Both rely on you determining the correct size of wire to be used. If I remember right, their will be two different wire sizes required, I just can't remember what they are! ... For short repairs, replace with the same size cable or add bigger cables for a quick fix.
To repair.....
Cut back the insulation on the wire until you find clean wire. This can be a bit difficult as corrosion can seep under the insulation. This corrosion causes the wire strands to blacken. It is possible to clean the wire with abrasive paper but this is very difficult to get around all the wire strands. Then....
1, use suitably rated crimp connections to extend the wire to the terminal points
or (as the connections are in a bad weather area!) better still...
2, solder the wire joints and cover with heat shrink insulation.

That should get you going for the next twenty years when a harness replacement is recommended!


M McAndrew

Thanks Mike I hope to get under the car again this weekend
GG Ginty

This thread was discussed between 04/04/2011 and 12/04/2011

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