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MG Midget and Sprite Technical - Another Electrical Starting Issue

Just under a year ago my 1500 suffered from the engine stalling as soon as the ignition key was released after starting, the problem was resolved after some good help on here from you guys and fitting a new ignition switch.

11 months later same problem, I presumed the new ignition switch had failed so Ive changed it for a new one today from different supplier and the problem is still there, the engine stops as soon as the key is released.

If its not the switch, it just leaves the ballast resistor and solenoid or is there any other possible culprit and any way to check the cause. I am not great at electrics or with a multi meter!
Tim Lynam

Tim, Certainly sounds like a possible ballast resistor issue-OR wiring
To test it-
Turn the key to the On-run position
With it like that you should have power on both ends of the resistor and on the power (+) side of the ign. coil

No power to resistor---wiring issue between ign switch and resistor (if there's power out of the switch)

Power on one end of resistor and not the other--dead resistor or connections

Power on both ends of resistor but not at coil -wiring or connectors
William Revit

Thanks William for your help, I have never come across the ballast resistor and it seems difficult to track down on some cars, if anyone has any tips on where it could be found on a very early 1500 (late 74) it would be appreciated.
Tim Lynam

On most 1500s (don't know about earliest 1500s) it was built into the loom as a Pink wire IIRC.
Rob
MG Moneypit

Thanks Rob, was it wrapped up in the loom or was it exposed?
Tim Lynam

Tim, have a look in the Archives I'm (almost) sure there are photos.
Nigel Atkins

Nigel, there seems to be several different types and positions in car depending on year and the ones you can buy are different again.
Tim Lynam

Tim

As Willy says. If you have a voltmeter/DMM place probes between coil + and chassis with ignition on. If you have 12v, your ignition switch might be intermittent but this is all unikely given your symptoms. I bet you'll have 0v at the coil. It then does point to the ballast resistor/ cable. I don't know what form that takes on a '75. You might have to bypass ignition switch to coil if ballast is in loom.
Bill Bretherton

Sorry Tim my memory was that the 1500s were the (pink) wire in the loom.

As your car is so early and has crossover features from the late 1275 does yours have a ballast for the coil?
Nigel Atkins

Bill, thanks I will check.

Nigel, when I swapped to electronic ignition I added a new coil suitable for a ballast resistor, but as you rightly say the car has 1275 parts & 1500 parts, but I presume there’s a resistor in there somewhere with the car running ok with the ballast resistor coil.
Tim Lynam

Fair enough Tim, looks like I remembered wrong about the photos, perhaps I was thinking of photos in the B section, and plenty of info on ballast on Paul's site.

Some info I found in the search which might help(?).

“A 1500 requires a ballasted coil. The ballast resistor is built into the +ve IGN feed to the coil (White wire).
If you fit a non ballasted coil you will get a weak spark and possible running problems.
This can be overcome by putting in a new IGN feed but you would also have to disconnect the 12v Starter 'Jump Feed' to the coil (White/Green wire).”


“I haven't seen a 1500 midget in a while, but if it is consistent (likely)with other cars like MGB, the ballast will be a braided fiberglass covered wire in the harness. There is normally an external splice point (near where the coil feeds emerge from the harness) where you can see White wires spliced to the fiberglass one, which may be white, red, pink, or brown (in my experience).”
Nigel Atkins

Tim. Is your system factory original? Many vehicles have been modified over the many years since the last ones were built and the starting place for any form of trouble shooting is to determine exactly what you are dealing with. Do you have a factory electronic distributor (Lucas 45 DE?DM 4) which might have been used on your vehicle or do you have a points type (Lucas 45D4). In 74 to 75 models, most of them used the Lucas 45D4, points type, distributor with the Lucas 45DE4 (Opus) system coming somewhat later and the final system, the Lucas 45DM4 being introduced in 1980.

Do you have a wiring diagram specific to your model Midget? The wiring diagrams changed, sometimes year by year. A copy of the correct diagram, enlarged on a photo copier, would be of significant use in your trouble shooting. I had mine laminated after enlargement so that I could trace the wires on the diagram using a dry erase marker.

You note that you have a "coil suitable for a ballast resistor" but you have not determined whether you have full time 12v input or whether the voltage is dropped down to a nominal 6v (average is about 8v in truth) when the ignition switch is in the "run" position. All of these are things you need to determine before you can effectively begin your trouble shooting to find and fix the problem.

There is a short article on trouble shooting the ignition system on my website at: www.custompistols.com in the MG section. That might provide some useful information. At the very least, it would allow us to, perhaps, determine what you currently have and discuss how to best go about checking out the various systems.

Les
Les Bengtson

Les,

The distributor is an AccuSpark distributor with electronic ignition and AccuSpark coil, I have never checked the voltage at the coil unfortunately so unsure if 12v or 6-8v when engine running. I know many do not like the Accuspark system but I have been very happy with it, or I am when the rest of the system is working!

Thanks for the link to your site, it has some interesting information.
Tim Lynam

Tim. I hope the information will be of use to you. I purchased my first LBC in 1968 and have owned and worked on them most of my life.

The "6 volt coil", designed to work with an input of between six and eight volts, when constantly fed a 12V input, will break down internally. This may be part of your problem. But, more research is needed. All we can say, at this time, is that the car starts, then dies when the ignition switch is turned from the "start" to the "run" position. Thus, there is a fault associated with something within the white wire circuit (power when the switch is in the run position). If we can determine what the root cause of the problem is, we can fix it. Assuming it is a single problem and now two or more problems piggy backing on each other.

Basic test: Put an ohm meter across the positive and negative terminals of the coil. Resistance for a 12 V coil is about 3.5 ohms. Resistance for a 6 V coil is about 1.5-1.65 ohms. Let us see which coil you have and do our testing from that point onwards.

Les
Les Bengtson

Not many 1500 midgets here but the only one I've seen had a white resistor block mounted cross wise up behind the ignition coil--I'll see if i can find a pic ofit
easy access, looked original but maybe not-
You're in good hands with Les, so i'll but out--You only need one cook
willy
William Revit

does yours look like this with the resistor behind the coil-------


William Revit

I'm not very familiar with 1500s at all but that doesn't look standard, for UK at least.
Nigel Atkins

Willy, no unfortunately I don’t have a resistor looking like that, there are some available to buy in the uk looking similar but mine is buried somewhere yet to be found.

Thanks for the assistance all, I’ll look to check voltage.
Tim Lynam

Tim. The ballast is part of the loom, wrapped up with all the other wires.
Rob
MG Moneypit

Les,

I am getting a reading of 1.6 ohms between the two poles on the coil with the ignition on. So from your notes I do have a 6 volt coil.

Rob, if the ballast resistor is in the loom I would have thought the easiest way would be to bypass with a new resistor rather than removing the dash and digging through the loom which is not a nice thought!
Tim Lynam

You don't need the ignition on to measure the coil resistance.
But you do need to disconnect the wiring to the coil first, otherwise you won't know what resistance you're measuring.
If you see what I mean.
Greybeard

Tim. Recruit the standard "lovely assistant", get out your volt meter, and start tracing what is happening. As others have noted, your Midget with the 1500 engine most probably has two input lines to the positive terminal of the coil (with the negative, or ground, terminal going to the distributor in some manner). Connect the negative lead of the volt meter to a good ground, touch the positive lead to the positive terminal of the coil and have your assistant start the car, noting the system voltage being input to the coil. Should be about 12.5 volts (at least 11.5V) when cranking. After the engine starts, your assistant should return the ignition switch to the "run" position and watch what happens to your voltage input. It should either drop to somewhere between 6 and 8 volts or it may cut out completely.

If it turning the key from "start" to "run" cuts off the voltage to the coil, you have a problem in the white wire circuit somewhere between the coil and the ignition switch. The first place to check that system would be at the switch to ensure that you have power to the white wire circuit with the ignition switch in the "run" position. After that, it is simply tracing the wire through the loom until you find out where the problem is.

If the wires connecting to the positive terminal of the coil show 6-8 volts and the engine quits running, you are going to have, most probably, a problem with the coil or the low tension (LT) side of the distributor.

The great thing about these cars is that, to a very great extent, anything that goes wrong can be diagnosed and corrected by the owner using minimal test equipment. Not something that can be said of modern cars. Good luck.

Les
Les Bengtson

Thanks Les for the great instructions, they are a great help.
Tim Lynam

After trying several different remedies to the non starting issue ie adding a new resistor wired in from a new live feed, the 1500 is still not starting and shows no sign of trying too.

I decided to go back to how the car was previously wired and also tightened up a possible poor terminal on the white wire connections to the ignition switch (one thick and one slightly thinner white wire on the same spade connector at the ignition switch) and tested the voltage at the coil, there is 12.8 volts on the positive side of the coil with 2 white & green wires attached and 12.7 volts at the negative side with 2 white and black wires connected with the ignition turned on.

When the ignition is turned further there is no attempt for the car to fire up, it just keeps tuning over.

On removing the HT lead from the coil to the distributor and checking for a spark against the engine block on cranking there is no spark at all, the same when trying a known to be working coil on the car.

I am now a little stumped on what to try next with there being power at both sides of the coil and the same with a coil taken off a running Midget, but no spark.

Does anyone spot anything incorrect in the above or anything I have missed in the checking process.

Thanks Tim
Tim Lynam

I think the Accuspark distributor uses a "hall effect" device in place of points. It will have a connection to both sides of the coil - check these. Now, if you hold the positive meter probe against coil -ve with other probe to chassis and push car along in top gear or turn crankshaft, ignition on, the meter should repetitively fall from 12.7v to zero/low volts. If not, either there is a connection problem to the distributor or the hall sensor is faulty.
Bill Bretherton

Thanks Bill,

When I first changed to the Accuspark ignition I had a similar problem getting the car to run and after contacting Accuspark they told me it required a live feed from the live side of the fuse box, this resolved the issue.

Unfortunately there is no connection from the electronic ignition to the coil, just the original connections from the wiring loom, sounds a good way of checking but will it still work with above set up?

I had wondered if the electronic ignition had failed but with no spark from the coil I thought the issue maybe before the distributor, but would be very happy to be proved wrong and hear the car run again!
Tim Lynam

Tim, when I said both sides of coil I meant that the dist. needed a positive feed (as well as coil -ve). That positive could be coil +ve or could be off a fuse, doesn't matter. But it needs it from somewhere. You could remove dist.cap and check for +12v with ignition on and to check internal connections anyway. However, this could be confusing because coil -ve will be alternately +12v and 0v depending on rotor arm position (but the positive feed will stay positive and the hall sensor needs it to work).
Bill Bretherton

Bill, thanks for that, all looks good with the electronic ignition connections but will check for power with ignition on
Tim Lynam

Tim. You note: "Unfortunately there is no connection from the electronic ignition to the coil, just the original connections from the wiring loom". There should be a wire from the negative/CB side of the coil going to somewhere on the distributor. Is there? The low tension portion of the distributor is simply an on/off switch (points, etc) with a timing feature (cam lobe) that serves to turn on a step-up transformer (coil) and release a high voltage spike through the high tension portion of the dizzy (coil king lead, dizzy cap, rotor, and spark plug leads).

You note that you do not have a spark with turning over the engine. Do you have power to the coil as the engine is being turned over? (No power in=no power out.) If you do have power in, with lead are you using to determine whether the system is sparking? The only one to use for this test is the center lead/king lead that goes from the center terminal of the coil to the center terminal of the distributor cap. Be aware that checking the spark plug leads is a later trouble shooting step, performed only after you have spark at the king lead. That is because you introduce three more variables into the system when you test a spark plug lead. Only use the king lead/center lead for initial testing.

So, we need to know which lead you are using for testing, if you have power to the positive terminal of the coil when doing your test, and where does the wire from the negative/CB terminal of the coil go. From there, we may proceed forwards in a logical fashion.

Think of how good you are going to feel when you get this figured out!

Les
Les Bengtson

Good news so far on the checks that Les and Bill have suggested, the results are as follows,

1, Test to see if power at coil when turning engine over at key = 12.2 volts at positive side of coil and 9.8 volts at negative side whilst engine being turned over.

2, Yes there is a wire entering the distributor from the negative side of the coil, there is power at the connection of the white/black wire from negative side of coil with black cable entering the distributor.

3, There is also power at the connection just before the distributor of the live feed which connects to the red cable which also enters the distributor.

4, On checking for power at the Accuspark electronic ignition inside the distributor, unfortunately both the black and red wires enter the electronic module with no bare wires showing, so not possible to get a reading, just a flicker of life showing 0.01 volts at a couple of the metal posts of the electronic points, but I am not confident to say there's no power & the module is dead.

5, To confirm the previous check on one of the HT Leads was the coil lead taken from the central connection on the distributor which showed no spark against the engine block when turning over the engine.

All the above tests where done with the ignition on.

I presume the above points to a faulty electronic ignition or distributor??


Tim Lynam

Slightly different, as it was with points ignition, but I once had an intermittent fault on the wire between coil and dizzy. It looked fine and the car ran well when cold. But the wire core was broken inside it's insulation. As the engine bay warmed up the insulation stretched and the wire sagged under its own weight, breaking the continuity. The car would misfire and stop but after 10 minutes cooling off time it would fix itself and work ok for a couple of miles. It took a bit of fathoming out to find that fault!I

So, maybe your module is ok, but the wire has broken inside?

Probably frowned upon, but I have used dressmakers' pins to pierce cable insulation when there was no wire exposed, and used my meter using the pins as contacts.
GuyW

>>>I have used dressmakers' pins to pierce cable insulation when there was no wire exposed, and used my meter using the pins as contacts.<<<

Guy beat me to it. My thinking exactly. Generally I seal the holes thereafter with a dab of Scotchkote.
Greybeard

Tim
You need to know if the distributor module is working. Ignition on. Connect meter between coil -ve and ground and turn engine slowly, as I said earlier. The meter should alternately indicate 12v and 0v if the module is working. The module acts like the points it replaced by repetitively switching coil -ve to earth (giving 0v) and to open circuit (or high resistance) giving 12v or so.
Bill Bretherton

I think maybe an indicator bulb across the coil may give a better indication of the switching action. A lot is going to depend on the meter used for the measurement and the sophistication of the electronic ignition. If it acts as a simple switch of fixed dwell angle then it should be easy to see it operating with a meter but if a variable dwell ignition I would expect the operation to be too short to register. If the meter has a frequency range that would likely be a better bet to catch the switching pulses.

Tim,

What meter do you have.
David Billington

Tim. Agree with Bill and David. An analog volt meter should act as Bill suggests, while digital volt meters may not. A test light is a good quick check and I have an inexpensive one in all of my tool boxes carried in various vehicles.

One test that I have seen recommended, but have not performed myself, is to detach the lead going from the negative side of the coil to the distributor. Then, hook up a jumper lead from the negative terminal of the coil, have an assistant switch on the ignition, touch the jumper wire to the block while holding the coil lead near the block. When the jumper wire is removed from making connection to the block, it breaks the circuit, which should induce a spark at the coil lead if the coil is operating properly. If you get a spark by using that method, the electronic ignition is the problem. If there is no spark, the coil would be the next item to check.

Les
Les Bengtson

Thanks All, I have borrowed a good digital multimeter which gives good accurate readings, but I also have an older analog meter which I can try the test suggested above as the old meter should show any loss of power as the rotor arm moves, many thanks for all the suggestions.
Tim Lynam

Tim,

You said earlier that when not cranking the voltage is basically the same on both coil terminals but when cranking the - drops to 9.8V which makes me think the the unit is switching but the meter can't respond quickly enough to show the whole picture. As you have a borrowed meter can you get an oscilloscope, that would provide a much better set of data to evaluate. You're not local or I would offer mine.

Have you checked the HT coil resistance and checked it isn't shorted to ground on the original and known to be good coil, might not be.
David Billington

Do you have the original distributor/points/condenser &c to try?
Greybeard

Thanks for all the suggestions.

I connected an analogue multimeter probe to the negative terminal on the coil and the other probe to earth, switched on the ignition and got a nice steady 10 volt approx reading, with dizzy cap off pushed the car whilst in gear closely whilst watching the multimeter and the reading never changed and there was no flicker of the needle at all whilst the rotor arm turned a full 360 degrees.

I presume there should have been 4 flicks of the needle from around 10 to 0 volts as the rotor arm turned, but there was not one.

Next step is to try a friends spare new Accuspark ignition module also for a 1500 and pray for a spark!

I do have the original distributor and I know many would have swapped that over by now but looking to try the new Accuspark first.
Tim Lynam

If you have an old transistor radio tune it to medium wave between stations and sit (the radio) in the engine bay. When the ignition fires you will hear it.
Rob
MG Moneypit

Rob, that is how I set static timing on my cars. Recommendation used to be to do it with cigarette paper between the points, though a light bulb would be more accurate
GuyW

Tim
It does sound like the ignition module is faulty (or a cable/ connection fault), but trying your friend's Accuspark module should verify this.
Bill Bretherton

The Accuspark module was changed and straight away the car sparked into life, so thanks all for the great help in pointing me in the right direction of how to test.

This was the second Accuspark module in around four years, the first failed due to the cable snagging in the distributor, my fault for not securing with cable tie, but the second one only a couple of years old and looks ok other than a tiny nick on the positive cable. Maybe time to purchase a better type than this cheap version.
Tim Lynam

Tim,
if possible why not just repair the nick and perhaps if suitable over sleeve to provide more protection and secure (allowing for movement internally) more externally. If the unit has been damaged then it is not at fault. Most now find them very reliable as they either work or not from early use.

To be fair to Accuspark your two sound like many other failures reported in that it was not the fault of the actual units but the installation.

The failure to secure is common but most people unlike yourself blame the unit rather than the installer or subsequent accident or carelessness.

Nigel Atkins

Nigel,

The first faulty module failed due to me not securing the two cables with the cable tie, the first one I did repair until fitting the replacement.

The second module was fitted correctly keeping the cables away from the spinning spindle at the centre of the distributor, I have no idea how the cable could have been damaged but there's only a very tiny nick which maybe I could repair but I no longer have faith in the unit or if the cable is the cause of a total failure, I have always defended Accuspark and never had too many issues with poor parts but only around a couple of thousand miles is pretty poor even if they are cheap.
Tim Lynam

Tim.
I was praising you and defending the Accuspark unit but I can't praise it as I've never had any Accuspark products other than their red coloured rotor arm (same as Powersparks) which was OK for the cost. Their spark plugs, HT leads and dissys don't appeal to me.

I had an Aldon igniter head and it was good but these units only deal with the top part of the dissy leaving the mechanical bottom probably worn. Even from the factory the dissys were off factory within a few years so after decades of use the bottom isn't going to be great even if still functioning well. You can get them refurbed by the Dissy Dr but I have no idea of cost.

When I went from existing dissy with Aldon to fully electronic dissy (standard 123) about 13 years ago the difference was noticeable and it has been fit and forget since.

Not a cheap option but the reliability has paid for itself let alone the (small) performance and starting and running improvement and consistency.

You can get the CSI, and if you have the need or want with immobiliser fitted (at extra cost), I'd not bother with programable, not needed.

https://csi-ignition.com/mg-midget/
Nigel Atkins

This thread was discussed between 20/01/2022 and 13/02/2022

MG Midget and Sprite Technical index

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