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MG MGB Technical - Starter run-on

Here's an odd one. When starting my 69BGT, I turn the key to the "on" position, let the fuel pump prime the carbs, and then turn the key to the "start" position. The starter starts to turn the engine over. If I release the key back to the "on" position, the starter keeps running. I can stop it by placing the car in gear (engine not started yet) and releasing the clutch which jerks the car forward a bit. The load from the transmission causing the starter to disengage and stop. Second oddity - from this point, turning the key back to the start position does nothing. I have to turn the key all the way to the off position and start the whole process over to engage the starter again. By the way, once I get the engine running, the starter will still be operating (high revs) for about 2 seconds before finally dis-engaging. The starter was replaced last year (rebuilt unit) and has always done this. I have a relay routed in the ignition wiring and have replaced the relay but that failed to fix it. Is the starter bad or is it the ignition switch, or both? Any advice or ways to troubleshoot.
D Gesse

Hi.

I suggest that you use a test light to see if the 12V remains on the starter relay white / red connection after the key is released. If it does remain, suspect the ignition switch (unlikely).
If it doesn't, repeat with the white / brown connection.
If the 12V disappears from the white / brown the problem is probably in the starter motor's solenoid.
If the 12v does remain on the white / brown, the relay is sticking.

HTH... Don
Don

Yeah...hard to tell if this is electrical (more likely) or mechanical. I did have a similar situation on an older Volvo, I own. Turned out to be a short between a couple of the wires involved way before they got to the solenoid/starter. I could stop it by pulling wire off the solenoid after the car was running. Got me home so I could then ask someone about likely cause. You might try that so see if it disengages it. Someone correct me if I am off base here on an MG.
J.T. Bamford

Whatever it is I would fix it soon before you eat up your flywheel.
Luigi

I had a problem with the brown/white shorting to the brown down by the starter. It only shorted twice. The first time I ended up chasing my B across a parking lot, the second time (on the way home) it engaged while I was driving along.

It killed the starter!!!!
Dauntless

Being able to disengage it by 'stalling' it seems to indicate a starter problem, particularly if it only started when you replaced the motor. But having to turn the key all the way to off before you can energise it sounds like a wiring/switch/relay problem, and is what 'new' cars used to do several years ago (and may still do for all I know) specifically in an attempt to stop you re-engaging the starter with the engine running.

You didn't by chance fit a rubber bumper starter with the two small spades - one the operate terminal and the other the boost terminal to the coil - and connect both spades together? That could account for the first part of the problem.

You need to work back from the starter with a voltmeter connected seeing if you still have 12v (more likely 10v) when you release the key, and have the battery ground strap ready for a quick disconnect. Start (ho ho) with the white/brown at the starter, then the samw wire at the relay, then the white/red at the relay, and the same wire at the ignition switch.
Paul Hunt

Thanks Paul for your suggestions. The starter does have a second terminal but it is a smaller spade connector and is on the same terminal bolt as the larger one. No wires attached to it though. The starter is a rebuilt Lucas unit.

As far as the ignition switch, I believe it is original, or at least, the previous owner has never changed it since owning the car since 1973.

Will check the wiring (especially my relay job) this weekend to see if its an electrical issue or if its the starter itself. Don't know if this happened with the original starter prior to replacement as the starter didn't work when I purchased the car - thus the replacement.
D Gesse

This thread was discussed between 13/04/2004 and 15/04/2004

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