1977 MG MGB Ignition/electrical

KNIEMANN

MEMBER
1977 MG MGB
90,324 MILES

For sometime now my car has been randomly shutting off while running. Seems that power to the ignition fails. I have a kill switch in line because the car didn't use to shut off with the key off. If I turn the switch off and the back on the car comes right back on. Also the gas gauge and temperature gauge comes on and shuts back off or doesn't come on at all for days. I was only shutting off a few times when it was cold and the it would stop doing it. Yesterday it started missing very bad and would not run. Today while testing the wiring it seems to be running fine but is still shutting off occasionally but after the miss firing yesterday the ignition light stays on when the car is running. It did not do that before only when key is in the on position and not running. The light is also flickering. I have also noticed power the vacuum advance comes on and off and have a similar problem with several other circuits including brake lights. It seems to me as the hot wires are grounding somewhere but I so far have not found a cause. Any suggestions?

1 Reply

HMAC300

MECHANIC
48,601 POSTS

First if you have the amplifier in your distributor get rid of it as they are junk and fail without warning. It's easy to tell as it's electronic inside dist with a large box outside of it. Check your ignition switch wiring as there are no fuses or relays protecting the headlights and if you have put halogen lights in headlights there is a good possibility that you have burnt the harness from ignition switch to headlights inside the car. Ground are the largest problem on these there is a ground cable actually about three right by the coil area on the fender under the hood, clean that and make sure they are good. Also check the one in the trunk under the trunk latch as well. I have an 80 and used to own a 78 so very familiar with these. You alternator may be going bad why the light is staying on after key shut off but make sure with that prior to getting another. I highly recommend getting the MGB electrical systems by Rick Astley. It's about $60 but well worth it. It covers early and late models and by section so you know what to check very easy for the beginner. It is possible that you may need to run a separate ground to one of the lights to work.