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MG Midget and Sprite Technical - Stubborn Ignition Problem

I have a 1976 midget with electronic ignition that had been running perfectly. Recently, I made multiple consecutive attempts (too many) to start the car. The starter motor engaged strongly each time, until it didnt. The final attempt resulted in the tachometer gauge moving wildly, no solenoid or starter sound and the smell of melting plastic when I popped the hood. The positive and negative battery cables were very hot as was the starter solenoid. I immediately noticed that the positive lead from the electronic ignition module had come loose from the coil. So, this explains why there was no spark and how I managed to break a perfectly good car. I disconnected the battery cables, replaced the very old battery, the starter solenoid and reconnected everything. The good news is that big short through the starter solenoid is cured, all wiring remains cool, but the solenoid doesnt click, and the starter motor doesnt turn when the ignition is engaged. The red ignition warning light comes on as normal, but that is as far as it goes. When the ignition key is fully turned, I read full battery voltage with a multimeter on the positive side of the solenoid and a test light gets considerably brighter when that tool is used. I have tested the solenoid outside of the car and it clicks rapidly when touched with positive and negative leads. I am at a loss to figure out my next move. I have a wiring diagram and suspect a damaged wire somewhere, but so far, no luck. Any ideas. Thanks in advance.
Steve
Steve Mauer

Hi Steve

A photo of the connections to the starter solenoid might help us.

Also, which terminal of the solenoid are you measuring full battery voltage on?
Dave O'Neill 2

Disconnect the white/green wire from the solenoid. This is the one that comes from the ignition switch. Connect one terminal of a bulb to this and the other terminal to earth. When you turn the switch to the start position the bulb should light. If it doesn't the wire is broken or the switch is faulty. A temp wire from the switch to the solenoid will tell you if it is former. Also check that the solenoid is making a good contact to the car body.

If you think you have problems think of me and my 2005 MG TF. The air bag warning light won't go out and it is controlled by a computer so a bulb and earth wire are no help.


Jan T
J Targosz

It should be a white/red wire from the ignition switch to the solenoid.
Dave O'Neill 2

White green is the ballast bypass wire when a ballasted coil is fitted, dumps full voltage to the coil while starter engaged.
Most solenoids have two small spades, one for the white red that activates the solenoid, the other for the white green as above (if fitted). Mix them up and it won't operate.

Jan T, have you checked & cleaned the connectors under the seats? Cause of 90+% of air bag light warnings. Next most frequent is the rotory coupling aka clock spring in the steering column.
Paul Walbran

Hi Paul,

Thanks for the message. Yes I checked the underseat connections and replaced the rotary coupling. I even found an auto electrician that still had one of the origial, dealer diagnostic computers. This showed un no faults but then a few days later suddenly the light started to work properly! Because of this problem, faults with the relays in the Pectron computer, having to have keys reprogrammed and having to bale out bucket fulls of water after rain (thank goodness for our Wet/Dry Vax) the TF has now been sold and replaced with the Sprite. No computer, no air bags, no central locking and no thick carpet underlay to soak up water. I have noted the price of Midgets and Sprites appears to be rising and a number of enthusiasts have said the smal size and simplicity appeals to them. It does to me.

Cheers

Jan
J Targosz

Indeed yes!
Old cars might get rust challenged, but complex electronics will be the death of new ones
Paul Walbran

This thread was discussed between 23/08/2021 and 25/08/2021

MG Midget and Sprite Technical index

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