'78 electrical gremlins

[Bilcast]

I am working on a 78 mgb and have the following electrical issue: car has a 5 second delay in shutting off except when you take the bulb out of the ignition light or put a test light on the white wire in the key switch. The anti run on circut is disconnected. it seems as if voltage is being supplied by another source. I am at a loss as to my next step

[Flash75]

If you don't have a manual with a good wiring diagram go here and select MGB
http://www.advanceautowire.com/indexb.htm
Locate and print the Late US Market MGB from Haynes wiring diagram. I don't know if your model year car had a EGR service reminder. If if did the diode shown just below the anti-run on switch could cause the problem. There is another diode in the brake light and handbrake area on the right side of the diagram. that diode could also case the problem. I don't own a late model car and don't know where the diodes are located. But to check the problem you need to open the diode circuit/circuits and see if that corrects the problem. Failure of these diodes is common. If bad you may need to find a generic replacement at Radio Shack or some other electronics store. Hope this helps.

Clifton

[KimMG]

The wiring diagrams at www.advanceautowire.com have been updated to include the more acurate ones from the Bentley manual. Some people have had enlarged copies made and laminated at Kinko's to make them easier to read and mark off circuits with eraseable markers that they are working on.
Make sure all your grounds are clean and secure so that there are no sneaks. Diode failure is common. It has been known for these cars to try and start themselves and run away from home when a diode fails.
Replacement wiring parts can be found at a variety of sources. Advanceautowiring.com, britishwiring.com, mossmotors.com and Radio Shack is a short list of suppliers.

[jimmy wade]

My delay is more than 5 seconds. I think the car would until it was out of gas. If I jiggle the key enough sometimes it shuts off. Most of the time I let out the clutch and choke it off.

[jimmy wade]

Put a diode on the brown/yellow wire going from the alternator to the ignition light. You can get the DIODE at Radio shack. I just ended a week long search for a way to correct this problem.

Once you cut the wire put the diode in the line so the ignition light burns with the key off. If the light doesn't burn, reverse it.

[fgwebb]

Jimmy Wade:

Can you expand on your instructions to install the diode. It would seem if your alt light was on when the key was off (and removed) you would have another problem with the light being on all the time. Do you mean with engine off - and key on?

thanks