Is there any way to easily (or with moderate difficulty) add an idiot light for the charging system when there is a voltmeter in the car already?

 

I should imagine it would be as easy as disconnecting the resistance wire, and adding the idiot light in it's place, as per the attached diagram (shows both options). Why would you want to?

Edit: Just noticed your other post about eating alternators - I guess you want one because you are worried you won't notice the volt meter drop when the alt pikes it next time?

 

Yep, every time I begin to trust the bird and forget to check the volt meter, it sinks it's talons into my butt.

Looking at your diagram, I can't quite see it well enough. I tried to find it in my vehicle service manual, but no luck. If you can tell me where to find that diagram, please do.

I think that shows a wire from the gauges fuse, through a bulb, to the brown wire from the alternator. The bulb then "compares" that voltage to battery voltage through the resistor wire, and if it is low enough, the bulb lights. But that seems different from what you say above. Please "enlighten" me.

 

Yeah, sorry it's a little non-explanatory. It shows both options connected simultaneously. Cars with the idiot light only have the bulb connected to the gauges fuse. Cars with the volts gauge (not shown on this circuit as it's not part of the charging) only have the resistance wire, in place of the bulb.

Sorry but I don't know where the resistance wire is located stock, somewhere in the cabin between the C100 connector and the ign switch. I think it may come off the back of the ign switch connector, but I've had a rhd conversion so all that's been chopped up. Mine was stuffed into a random part of the harness on the lhs.

If you can't locate it, you could always cut the brown wire at the alt pigtail, and run a seperate wire back into the cabin, thru a bulb and fuse to an ign run source.

Edit: Actually just thinking more about it, probably both the idiot light and voltmeter versions have the resistance wire - but it's just necessary for the voltmeter version only. It will have no adverse effect on the idiot light version, so they probably used the same circuit/harness for both.