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MG Car Repair/Starter motor turns unaided


QUESTION: My vehicle is a  2cv Special. The ignition switch appeared to be faulty  recently and didnt cut out the power to solenoid when it should  . but after replacing with new switch it did the same and engine continued to turn over . So i switched off the emergency cut-out . I read Howards reply to this problem on an Mg . Maybe the fault is the same with the wiring to solenoid or could the regulator wires be mixed up accidentally ?
Regards Aidan

ANSWER: Hi Aidan,

Most all cars either activate the starter solenoid by either a power sent to it by the ignition start position or by a relay which itself is activated by the start position of the ignition switch.

In these cases a solenoid is held in the active position by a power source even when the key is released back to the run position. However, there is another possible. The solenoid itself can stick in the active position and thus keep the starter engaged.

Here is how to test the system. You will need a 12v test light or a volt meter.

Go to the starter solenoid with your test light or volt meter and ground the negative lead of the volt meter or the clip of the test light which ever you have. Have someone try to start the car and as soon as the starter sticks "ON" and the key is back off to the run position, quickly while the starter is still spinning the engine test for power on the small terminal on the solenoid to see if it is powered.

If the small terminal on the solenoid is a push on flat spade connector you don't eve need a test light nor a volt meter at this test. Just pull the small wire off of the solenoid and if the starter stops turning the engine then the problem is back at the switch or a relay if the car has one. If the starter keeps running with the small wire pulled off then the solenoid is the problem and it is stuck or or faulty. If it is still turning the engine you can also tap on the solenoid lightly with a small hammer and if it then stops it is a sticking solenoid and since solenoids today can not be taken apart you still need to replace it.

In some cases a starter motor can draw too much amps and thus burn the contacts in a solenoid and make it stick.

If however, when you removed the small wire it shut down the starter then you need to look at a wiring diagram of the car to see if there is a relay or not as a relay can also stick the contacts and make a starter keep running.

I can't tell you if it has a relay or not because I don't know want a 2cv car is. But that don't mater because all cars do it the same way.


---------- FOLLOW-UP ----------

QUESTION: Thanks Howard , well explained( . A 2cv is a French Citroen car with air cooled 2cylinder 600cc engine.mine is home made so has no wiiring diagram. )I will try your test first with voltmeter. There is a small slim rounded aluminium box with 3- 4 wires behind dashboard looking old . This might be the relay . I think you are saying not to open the solenoid which sits atop the starter.? The starter motor you suggest could be be the culprit.
Thanks for your help . Much appreciated and so quick reply .
Regards Aidan

Yes, the solenoid does sit on top of the starter motor and do not try to open it up at this time.

Get a 12v test light (available at most auto parts stores and very inexpensive) Then connect the clip lead to any bolt on the engine block or head (a ground) Then with the point of the probe, touch the small wire contact on the solenoid.

(There should be 3 posts on the solenoid, two large ones and one small one.) One large post should have a heavy gauge cable going directly to the battery and the other large post should be connected to a cable or strap going inside the starter motor. The small post on the solenoid should have a small gauge wire on it and it is the "Trigger" wire that activates the solenoid when the key is turned to the "Start" position.

This "Trigger" wire is the one you need to test with the test light. You must know if it is powered at the wrong time (when the key is released back off of "Start" position)

Do not replace any part until you test and know for sure what is wrong. You can only know by testing with a test light.

All tests must be done in the failed mode. (when it is stuck in the starting mode)

It is unlikely that the starter motor is at fault, but testing is the only way to tell.

Run this one test of the "Trigger" wire post first and let me know the results. Then I will give you the next test.


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Howard M. Fitzcharles III


MG from 1956 (USA versions only) up and Engine theory.


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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