Red ignition light comes on when ignition turned off

[Charlie1066]

I believe that this is probably an alternator issue, but just in case, if anyone here has encountered the same problem. It is a 1700 1994 xflow - used daily. Just started doing this. Battery now flat. Basically, when I turn the key to turn engine off, the red ignition light comes on. Even when I take the key out. When I could start the engine (before flat battery), the light went out. 

Help please...

[Jonathan Kay]

That's very interesting.

Check fluid level in battery if appropriate.

Do you have a multimeter and would you like the wiring diagrams for your Seven?

Did it used to work normally? And has there been any work on it or anything that might have caused the change?

All other electrics working OK? Is anything else that should only work with the ignition ON working with the ignition OFF?

How many wires of what colour connected at the alternator, and do they look OK and feel tightly connected?

Ditto at the ignition switch. And does it have an additional starter switch?

If you can get it started what's the battery voltage at 3,000 rpm?

Jonathan

PS: I don't like guessing causes, but someone's going to suggest this anyway, and this might save time. If it's the diode pack in the alternator that has failed it might be replaceable without buying a whole new alternator. Is there anywhere on Jersey that does this sort of work?

[Jonathan Kay]

Here's the simplest possible generic circuit for an alternator warning light:

Jonathan

[Nigel Fox]

Sounds like a faulty ignition switch to me.

As in Jonathan's diagram, the ignition switch contact closes to put a 12V supply to the lamp. If that contact is stuck closed you will have the fault described. If the contact is open I don't see how an alternator fault could light the lamp.

[Charlie1066]

Thanks Jonathan and Nigel. I will check amps later. I have a spare battery so can start her. Happened when I parked up on Saturday. No issues before. Car starts fine if battery charged. Goes flat as the red light stays on unless I disconnect battery! 

[Jonathan Kay]

"Sounds like a faulty ignition switch to me.

As in Jonathan's diagram, the ignition switch contact closes to put a 12V supply to the lamp. If that contact is stuck closed you will have the fault described. If the contact is open I don't see how an alternator fault could light the lamp."

 

Yes, I agree how about how it could be caused by a fault in or near the switch.

 

But there are reports of the same symptom from failed alternators. And this could be a failed alternator. My current thinking is that when this happens there is a short in the diode pack or similar and the electrons find their way through the ignition switch and the long way round through some circuit or other and thus to earth. Although the diagram shows nothing else connected to the switch that isn't actually the case. (If this is the explanation it would be rather like the funny circuit for the indicator warning light in Sevens that only have one.)

 

This might just be the chance to test that explanation!

 

Jonathan