MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Won't Start

I have just purchased a well used '71 MGB-GT. It ran great for 3 days until I took it for a short trip in rainy weather. At the first stop it would not start again. Just an audible click from the starter relay and nothing else. After a three tries on the ignition the battery died.

Charged the battery after a tow back to the garage. I checked the connections to the relay, starter, alternator, and coil and they seem fine. I did cause it to turn over by accident when I was reconnecting the start solenoid and crossed wires. However, same results from the ignition.

I'm ill-prepared for electrical difficulties but have ordered a good multi-meter and an additional shop manual.

Any advice or suggestions would be appreciated.

Cheers.
Rob

Rob,
You might have a bad solenoid, but would first try cleaning all of the wires/connectors at the starter. You should also clean and dry out the inside of your distributor cap (and plug connectors). Buy yourself one of those cheap 12V test probes at your local WalMart. You know, they look somewhat like a screwdriver with a sharp tip on one end and a clipped wire on the other (bulb in the handle). Turn on your ignition and you should have 12V on the positive side of your coil (white wire). Great thing about B's, assuming fuel and ignition system are all OK, is that they can be easily started with a short push and popping the clutch in 2nd gear (make sure your ignition switch is on when you try this). Many years ago (39), while wintering in Maryland, a push-off or a hill coast was the only way I could start my '66.
Steve Buchina

Any problem that meant power wasn't being connected to the starter wouldn't in itself flatten the battery. If the battery really *was* flat then maybe it is a non-charging problem - it was running down while you were driving it, and eventually there wasn't enough charge left to power the solenoid.

With the engine running at a fast idle and with minimal electrical load check the voltage on the brown at the fusebox, you should see about 14.5v. Now turn on headlights and it will drop a bit but should still be above 13v.

You can also get apparent battery failure if there are bad connections in the battery ground strap, the battery 12v connection, or where the battery cable and browns terminate on the solenoid. You can check these by connecting a voltmeter between the battery 12v *post* (not conenctor) and the stud on the solenoid and measuring the voltage while cranking (disconnect the coil -ve terminal). Likewise measure from the battery ground *post* and starter body. Ideally you will only see a couple of tenths of a volt in each 'leg', but I have seen as much as 3v lost. Anything over 1/2 volt is worth investigating and cleaning all the connections.

There can be other problems with relays, solenoids, starter motors and connections between them that affect cranking but won't flatten the battery. Of course you could have more than one problem, especially on a car new to you!
Paul Hunt 2

Update. Got my trusty multimeter today. First I checked some fuses and replaced two. Then I cleaned all the contacts at the starter solenoid.
I'm reading 13v at the battery and starter solenoid and up to the first fuse with the ignition off.

If I turn the ignition on the battery is at 13v but the meter reads 1.6v at the solenoid 1.5 at the first fuse.

The battery does seem to hold it's 13v but I've tried cleaning several contacts etc. and can't seem to get above 1.6 at the solenoid with the ignition on.


I tried roll starting but that failed. I'm thinking there was not enough power to get the fuel flowing. I'm going to go collapse now since pushing it by myself was exhausting for a guy who sits behind a desk all day.
Rob

Did you check your ground (-) strap?
.

There are no fuses in the ignition or starting circuits - in factory wiring anyway.

If the voltage on the brown on the fusebox (bottom front) is what drops from 13v to 1.6v then as I thought, a bad connection somewhere, which is causing the majority of the battery voltage to be lost across it rather than reaching the solenoid. At 1.6v there won't be enough to power the ignition *or* the fuel pump.

With the ignition on measure the voltage between the battery ground post (not the clamp) and clean metal on the body. If this shows any voltage at all the battery ground strap connections to body to battery, or both, are bad.

Then do the same between the battery 12v post and the brown on the fusebox. This also should show no voltage. If it does then either the battery clamp or where the browns joining the battery cable at the solenoid are at fault.

Very important! Before taking any tools to the 12v post of the battery or the solenoid disconenct the ground strap from the battery.

At the solenoid you may either have the battery cable on the solenoid stud and the browns on one or more spades, as was earlier practice, or have the browns and the battery cable all bolted onto the solenoid stud which was later practice. Remove and clean all of them, and if the connectors aren't a firm push-fit on the spades pinch them up a little bit with a pair of pliers.

You mention 'the battery', a 71 would originally have had twin 6v batteries of course and a link cable. If you still have these then also measure between the posts that carry the link cable between the two batteries.

Don't replace the battery ground strap until you have finished working on the 12v connector, link cable, and solenoid.
Paul Hunt 2

It's Alive! Sort of... A close examination of the wiring diagram in two different shop manuals (Haynes and Bentley) showed me 3 brown wires at the starter solenoid (also the brown-white and the black battery cable). However, my car actually has 4 brown wires (6 total). Strange, but probably just a wiring harness mistake by a previous owner. After a long process of elimination I narrowed the problem down to one of these brown wires. With the key on I had 12.7v everywhere until I connect that last wire and then everything drops to 1v. Of course it's the one that connects to the ignition, light, and fuel pump. After cleaning, checking and testing at all of these destinations I finally have solid 12.6v everywhere I'm supposed to with the key on. It was wonderful to see lights again with the key on.

The moment of truth - the first attempt at starting after my success- CLICK, nothing! Just a small click from the general area of the starter relay and nothing. However, the good news was that power was still good all around, no power drain. I did a quick and dirty hot wire and it fired right up. I promptly kicked out the jack stands and drove it around the block.

At this point I'm thinking I'll have to replace the starter relay. I hate to spend the $70 but that's gotta be it right? Is there an easy way to verify that it's bad?

As a side note, I'm definately going to be putting new wiring everywhere. I was finding cracks and ugly wires everywhere.
Rob

Rob,
Glad you got it running. Would suggest that you don't rush out (just yet) and buy a new relay. Continue with your wiring clean-up. A Dremel tool with a small wire wheel brush is very useful in removing the oxidation from your bullet connectors. For the female connectors, I use small caliper (e.g. .22 cal.) gun barrel brushes. Another area that you should concentrate on is all of the ground connections - there are a number of them in your car. The primary is a braided wire strap that bridges the engine block to one of the motor mounts (usually on drivers side). Some B's will have a second ground strap between the transmission and its cross member brace. Make sure these are clean. Secondary grounds are recognized as a bundle of black wires attached (screwed) to the body. These can be found in the trunk, under the dash and under the hood (e.g., firewall, inner fenders and behind grille. Don't forget your fuse block. Remove and clean thoroughly. If you are still concerned about your starter, remove it a take it to a starter/alternator rebuild shop. Have them test it - it might only need internal cleaning. I've been using a local shop here where I live for over 35 years. A total rebuild (with new solenoid) runs just a bit over $60 and the the unit looks brand new and come with a one year warranty.

Check out ebay - they are a great source for MGB parts (used, NOS and new).
Steve Buchina

Where did you hot-wire from and to when cranking it? If it definitely is the relay you can hear clicking then there could be two or three connections which could be bad as well as the relay, so you should eliminate these first. It could also be a solenoid fault.

It's basically doing much as you did before, measuring the voltage on various connectors before and during attempting to crank.

The relay has a brown on one side of its contact, and this should show battery voltage at all times. Make sure it does so without cranking *and* when the key is turned to crank. Check on the relay spade as well as the wiring connector.

Next check on the white/brown (or brown/white) wire on the relay for 12v when you turn the key to crank, but not normally. Again check on the spade as well as the wiring connector.

If you have 12v on the brown spade when cranking, but not on the white/brown spade, then the relay *is* faulty. If there is 12v on the brown connector normally but not when cranking then the problem lies back towards the solenoid, although this is unlikely. On the brown connector but not the spade, or on the white/brown spade but not its connector, is bad connections between relay spade and wiring connector. Finally measure on the white/brown connector and spade at the solenoid during cranking. If on neither, but up at the relay was OK, then the wire is broken between the two. If on the conenctor but not the spade then a bad connector to soade connection as before. If you have 12v on the solenoid spade but it doesn't operate, then the solenoid is faulty.

And if it is the *solenoid* you can hear, then either the solenoid contacts, the starter motor, or the link between them are faulty. But some of those may be excluded by what ever you hot-wired from and to.
Paul Hunt 2

If your starter relay is bad you can replace it with a common Bosch type 4 spade square relay. They cost less than $10 in most automotive stores. Most of them are rated for 30 amps.

Clifton
Clifton Gordon

Update: To get it started I bridged the gap on the starter solenoid. Touching the brown to brown and white connections with a screwdriver. Ugly but effective.

I have also noticed a lot of clicking that seems to be comming from the fuel pump? As soon as I turn the ignition on there are several clicks about 2 seconds apart - sounds like the fuel pump or battery? I replaced the battery out of frustration (it was over 2 yrs old and had sat for a long time before my purchase). No changes in syptoms of course.

I did test at the starter relay while cranking. I got 12v on brown before 0v on brn/white. While cranking brown dropped to 0v and brn/white stayed the same. This was on the wire as well as the spade.
Rob

Rob. Yes, the fuel pump clicks until it has pressurized the fuel system. Then, it quits until it needs to deliver more fuel. This is not a problem.

The brown wires are always hot. That is why you disconnect the battery before working on some portions of the car's systems. It sounds like your problem may be a bad connection at the main terminal of the starter, a bad cable, or a bad connection at the battery. I have seen all three over the years.

One good test is to hook a jumper wire up to the large terminal of the starter and run it into the passanger compartment. Connect the wire to the positive lead of a volt meter and the negative lead of the meter to ground. You should show at least 12.0V and 12.5 is better. Then, turn the ignition switch to the start position and read the voltage. If it drops below about 11.5V you have a problem at the connection, in the cable, or at the battery connection.

Les
Les Bengtson

If the brown at the relay drops to 0v when you try to crank, and that was the case both on the relay spade *and* the connector on the brown wire, then there is a bad connection back through the brown circuit. On a 71 this seems to come via the two browns on the fusebox and then back to the solenoid. If there are two *separate* browns at the fusebox do the same test on both browns wire connectors and both spades at the fusebox.

If they *all* drop to 0v when you try to crank, or if the two browns are in the same wiring connector, the problem is where the browns join the battery cable at the solenoid. If by spade connectors make sure the spades themselves are clean and the connectors a firm fit on them, pinch them up a bit with a pair of pliers if not. The later arrangement of bolt-through connectors on the browns is much better as they all bolt up much more securely onto the battery cable stud. If this is what you have already, remove all the cables, clean up the connectors to shiny metal, make sure the base of the solenoid stud is also shiny, and reassemble with copper grease or similar. But before working on this terminal remove the battery ground strap first, and only replace it when everything is back on the solenoid and tightened up.

If there are two separate browns at the fusebox and one of them stays at 12v when attempting to crank then the spades or connectors at the fusebox need cleaning up and/or tightening up as above.

Whilst it is normal for the fuel pump to click a few times after being parked for some hours, especially if parked when hot, these would normally be rapid clicks, several a second, but only for a couple of seconds until the float chambers are refilled and the line pressurised. If it then continues to click once every couple of seconds, in fact if it clicks more than onece every *30* seconds, it implies either the carb float valves are not shutting properly and flooding the carbs or the non-return valves in the pump are leaking back. The float valves can be checked by removing the overflow/vent pipe from the float chamber lids and looking for fuel. It may take up to a minute or more for fuel to start leaking, depending on how bad the valves are.
Paul Hunt 2

Ok, now I'm really confused. I attached a wire to the fuse box at the brown spade (pos. 7 on the diagram) to check for a voltage drop from inside the car as I turn the ignition. I had no voltage drop on either brown wire at the fuse box.

Just for grins I thought I'd try to hot wire start the car and I touched this wire to the brown/white wire on the starter relay. It fired up so that's good. At least I know the brn/wht wire from the relay to the starter is good.

I then thought that this should work in the same way if I connect the brn wire at the starter relay to the brn/wht wire. However, it did not. I tested the voltage on the brn wire at the relay and found it to be the same as the voltage on the fuse box. I tested all of this at the spades and just the wire. I also tried the voltage at the relay brn wire during cranking and found that the voltage stayed the same this time. I guess maybe some of the contact cleaning I did worked.

I thought it was very strange that the brown wire at the relay could not start the car when crossed with the brn/wht since it supposedly comes directly from the fuse box. I would suspect a bad wire but wouldn't the voltage be off? Is it possible the voltage is high enough but the amps are not? I think it would fry my multimeter to test this during a start attempt so I havn't tried it.

Anyway, I think I've got it narrowed down to the relay/ignition circuit. One other change that's happened since I cleaned a few contacts and installed that new battery: There isn't a "click" anymore when I try to crank it over.

Does anyone know a Bosch model number for a relay like the one Clifton Gordon mentioned? I would be happy to spend $10 to eliminate the relay from my list of suspects.


Thanks for everyone's input and help!
Rob

From your post of 8th November the voltage on the brown at the relay *is* bad. If you can link a brown at the fusebox to the white/brown (or brown/white) at the relay and that causes it to crank, then the voltage getting to the fusebox is good. You don't say for sure whether there are two separate brown connectors at the fusebox, or just two brown wires in a single connector, but you do say the voltage didn't drop on 'either' brown wire at the fusebox, which implies two separate connectors. Did you test on the two spades (which *will* give the same voltage)? Or the two connectors on the wires (which could give different voltages)?

Whichever, you have proved the problem to be the wire between the fusebox and the starter relay, which is all of six inches. Factory wires are spot-welded onto the spade connectors which makes them highly unlikely to fail, but if you have PO or aftermarket wiring with crimped or soldered joints between wire and connector instead of spot-welds these could also be the cause of bad connections, as well as the wiring connector on the spade.

With the key turned to 'crank' measure the voltage on the fusebox spades *and* connectors, and the relay connector *and* the spade.
Paul Hunt 2

Just to add a note - a wire that indicates full voltage on your meter can fail instantly under heavy load. A case in point: the engine ground strap. It's possible to find correct voltages throughout the whole car without a ground strap. Yet such a car won't start because the other sources of engine ground (heater control and choke cables!) can't carry enough amperage to run the starter. I'm not suggesting that is your problem; with a bad ground strap, your starter wouldn't function when you touch brown/white to brown. Just bear in mind that your voltmeter doesn't tell all...

FWIW,
Allen
Allen Bachelder

That's the point of measuring the voltage with the key turned to 'crank', precisely to put it under load and reveal bad connections.

But with a bad *engine* ground strap even that test wouldn't show a voltage drop when attempting to crank, unless you used the engine as the ground and not the body or battery, and then it would only reveal it by the enigine *rising* to 12v, not the brown dropping to zero, i.e. you would still get 12v on the brown and brown/white at the starter relay (which Rob didn't get). And in fact there are usually enough ground paths via heater, accelerator and choke cables to allow the starter to crank with a bad engine ground strap, albeit slowly, and at the cost of cooking said cables.
Paul Hunt 2

Ok, very sure it's the starter relay now. I've fixed the brn wire that goes to the relay and tested the red/wht wire (shows voltage during crank). If I connect the brn/wht with the red/wht and crank it starts. With everything connected to the relay it clicks but doesn't start.

It occurs to me that this thread has gone on for several days and I should probably explain that there's a new baby in the house. I've really only had stolen minutes here and there to do the diagnosis and repairs. However, with everyone's help, I think it's nailed down! Thanks everyone! I'm sure I'll be back as I continue to clean up this somewhat rough car.
Rob

Connecting the red/white to the white/brown *would* still allow it to crank (at the expense of stressing the ignition switch) if the brown feeding the relay were faulty as your tests showed. As would the relay being faulty. If you now have 12v on the relay spade carrying the brown wire when cranking, but not on the white/brown, then the problem *is* now the relay. But I do find it doubtful that both the brown wire and the relay seem to have failed at the same time.
Paul Hunt 2

This thread was discussed between 30/10/2006 and 12/11/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.