Starter engages when ignition turned to on.

Technical MGB discussion
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Posts: 2
Joined: Tue Jun 02, 2020 8:09 pm
Forename: Dave
Surname: Laverty

Starter engages when ignition turned to on.

Post by Lavo01 » Sun Dec 27, 2020 2:02 pm

Hi everyone, this is the second topic I have started regarding my ignition system due to My own stupidity. A few months ago, the ballast wire on my. 1977 MGB overheated and melted causing starting problems. With the help of this forum I managed to sort this out. Whilst carrying out this work, I noticed that the previous owner had replaced some of the wires in the ignition system with anything he had to hand so I decided to change these wires with the correct colour coded ones and also fit an electronic distributor while I was at it. I did the retiring and fitted the new distributor but unfortunately, wired the distributor up to the wrong terminals on the coil which I believe fried the electronic distributor module. I replaced this with my old points distributor and as soon as I turned the ignition key to the on position, the starter motor engaged and would not turn off. I have checked my wiring re the wiring diagram and with previous posts re this and the wiring seems ok. I have replaced both ignition and starting relays with new but no change. I even replaced the starter switch with a new one but still no change. I'm currently running the car without a ballast resistor. Any help would really be appreciated as Ian totally flummoxed. Cheers.

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Michael Barclay
Posts: 81
Joined: Tue Dec 06, 2016 8:05 pm
Forename: Michael
Surname: Barclay
Location: Abingdon

Re: Starter engages when ignition turned to on.

Post by Michael Barclay » Sun Dec 27, 2020 5:09 pm

Hi Dave
Wow looks like you have had some real fun with the electrics on your car. Without seeing the car I think this is not going to be an easy fix but let try.
You mentioned the ballast wire burned out on your car. This is a pink wire that runs in the loom to the front of the car, across the slam panel and appears over on the driver’s side near the N/S horn. It then comes back as a White/light green wire to the coil. Have you checked the loom for damage all the way down and across the slam panel?
You also mention you are running with no ballast resistor. The original coil is designed to run on 6 Volts and is only supplied with 12 volts when the starter is engaged. Have you changed the coil to a 12 v non ballast coil?
Now to the starter engaging all the time when the ignition key is turned. The starter solenoid is powered from the starter relay which in turn is powered when the ignition switch is turned to the start position. So somehow power is getting to the starter solenoid. You mention you have replaced the starter relay so assuming it is not faulty can be eliminated for the time being. I would however double check the wiring to the relay to ensure you have connected the relay coil and main contacts correctly. Main relay contacts should be pin 30 brown wire. Pin 87 white/brown wire. (It doesn’t if they are the other way around) Coil should be connected pin 85 black wire and pin 86 2 x White /red wire. (It doesn’t if they are the other way around.) Try pulling the white /red wires off the relay terminal and see if the starter stops engaging. If this is the case, it’s possible you may have connected the white/red wire to the wrong terminal on the ignition switch when you replaced it. There is one other possibility. You will see there are 2 x white /red wires connected to the relay coil. As mentioned, one goes to the ignition switch, the other goes via a diode to the brake warning circuit. If the diode has gone short circuit, the brake warning circuit could be applying 12 volts to the starter relay giving the symptoms you describe. A multimeter should help with the above.
Hope the above is a starting point for fixing your problems.
Best regards
Mike Barclay

Vic Butler
Posts: 565
Joined: Wed Dec 21, 2016 6:07 pm
Forename: Vic
Surname: Butler
Location: North West Hampshire

Re: Starter engages when ignition turned to on.

Post by Vic Butler » Sun Jan 03, 2021 7:38 pm

The 12v supply to the coil is operating only when the starter solenoid engages. When the engine starts and the key released the "run" relay is activated and the start relay switched off. The coil is then running on 6v via the resistor..
Only the 6v supply comes from the relay so in theory the engine can't run once the key is released unless the ballast resistor circuit is complete. The 12v supply is directly from the starter motor.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine

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