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MG MGA - Where's the bad earth?

If I switch off the panel / dash lights using the P switch, the ignition light comes on at about 50% intensity

Any suggestions as to the culprit / cause?

Thanks
Dominic
dominic clancy

Is that with the sidelights and/or ignition switch on?
Lindsay Sampford

Dominic

You had an issue with the second horn you wired in. Is there a common (pun) wiring issue here?

Steve
Steve Gyles

Dominic, does operation of the rheostat make any difference?
Neil McGurk

I still haven't got round to the second horn, (still catching up at work from 3 weeks flat on my back (and not under the car))

It happens whether ignition is on or off. Also on sidelights whether headlamps are on or off (didn't test low / high beam). Happens when engine is running (ignition on) or not (ignition off)

As soon as the rheostat is not in the "off" state, the ignition light goes out. It's not going brighter or dimmer with the rheostat, it's either on (rheostat off) or off (rheostat in current-bearing mode)
dominic clancy

That is wierd Dominic. I have been studying the diagram for some time and cannot see how a bad connection of any type can give you that symptom. It has to be a contact between one cicuit and another, but even that is hard to imagine. The ignition warning lamp should be completely insulated from the body of the tacho it pushes into, one side of the lamp is effectively at earth, so the other side is looking for a battery, which normally comes from the ignition switch when it is turned on. Your ignition warning lamp is somehow receiving a low power battery supply on its non-earthy side when your sidelights are turned on. Maybe we are looking at more than one fault. Do your panel lights come on when the sidelights and the "P" switches are turned on?
Lindsay Sampford

The panel lights do operate correctly, except for the lamp in the speedo (which is where the ignition light is)

I'll check the other bulb this morning


dominic clancy

Are the bulbs swapped over with the ignition one blown?
Neil McGurk

That would certainly be a possibility Neil, if it wasn't for the fact that Dominic says it only lights when the P switch is turned off.
Dominic, has it ever worked properly? Has the fault only been there since a re-wire? This is starting to feel like one of those quiz programs!
Lindsay Sampford

Solved. The gauge earth tag itself had not been mounted when I refitted the speedo when I got it back from repair.

And I apologise, it wasn't the ignition light but the high beam light, so sorry for leading the sleuths on the wrong trail.....

And I still haven't fixed the horn. (Must leave something to do for the winter).

I have just bought a second engine for recon, and an early B overdrive gearbox, so that may be the major project for the winter. Now looking for a propshaft to go with the box, so if anyone has one lying about...


dominic clancy

This thread was discussed between 15/07/2009 and 16/07/2009

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