• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Ignition/fuel circuit suddenly off

Share this page

Sebring222

Sebring222

Senior Member
Country flag
Offline
Had a new one today in my 1974 CB MGB GT. On the way home, the car was driving just fine, I slowed down for a traffic light and the ignition/fuel pump just turned off. I had power, lights, starter, etc. but the alternator light did not come on and I had no ignition and no fuel pump. I had to be flat-bedded home. Any ideas what may have caused this problem out of no where? Absolutely no other problems, car was running and starting just fine until this incident.

Jim
 
The white wires off ignition switch (terminal 3 in your wiring diagram) feeds alternator warning lamp, coil, fuel pump, should have lost turn signals, brake lights, reverse lights and gauges, too.
First thing I'd be looking at was ingintion switch or the wires into it, especially white wires, since you have starter.
 
The fuel pump comes off the ignition switch before the fuse box, as does the coil....so if the fuel pump quit, probably not the fuse unless it and the ignition coil have been re-wired from original (possible).
If the fuel pump has been re-wired to the load side of the fuse, then the load of it could have popped the fuse, but that still leaves the alternator lamp which is direct off the switch, no fuse.
 
I've removed the cover for the ignition switch assembly. All the connections are good. Power to radio, horn, starter, wipers, but no power to ignition circuit, turn signals, fuel pump.
 
Got it! Simple movement inside the plug connector between the harness and the ignition switch shut down the ignition circuit,
fuel pump, etc. There were no faults, no broken wires, nothing visible to give any indication that there was a problem. It immediately started right up.
 
Probably the connector inside the plug has failed, or is in the process of failing.
Age, vibration, Lucas, heat, not necessarily in that order.

For reliability I would pull the plug off the switch, inspect the switch end for burning or overheating, and looseness, then retract the lock for that connector and pull it back out of the socket, and have a close look.

If it's what I think it is, based on old memory, where the metal part curls around is loose, or failed. etc.

If just loose, a slight re-compresion will work.
If cracked, broken, burned, etc, replace it.
 
As long as you fully understand what you just did is called a "wiggle test". Generally, there is no such thing as a "wiggle repair". The "test" portion is to guide you to where the "repair" portion needs to be done.
 
Back
Top