What is D+

[Peter M]

The regulator is inside alternator.

The alternator should pick up its earth if using the standard supplied alt bracket via the tension adjusting bracket.

Sam the ignition light should not be lit with the brown/yellow wire disconected from alternator,this suggets that there is a short on this wire .

[Blatman]

And because it hasn't been spelled out in so many words, and for my own peace of mind, just in case we're dancing around a fundamental error...

The ignition light is wired with two lives, one switched with the ignition, the other is the brown/yellow wire from the alternator. The brown/yellow wire from the alternator provides an earth to illuminate the lamp until the alternator starts spinning, after which it provides 12 volts to the lamp. The lamp now has 12 volts arriving at both terminals and because there is no earth to complete the circuit, it goes out and enables the charging circuit to energise.

As a secondary function, if the voltage from the alternator drops below a certain amount, the ignition lamp will glow or illuminate, giving warning of a possible alternator fault as the voltage across the bulb is no longer equal and some charge is going to earth, completing a "normal" circuit and thus illuminating the lamp.

[Peter M]

With the brown/yellow wire disconected from alternator with ign on, is the ign warning light lit .

Blatman

I asked Sam this question and the answer was yes.

There seems to be a problem here as the lamp should not be lit if brown/yellow is not connected to alternator, unless there is a short on this wire.

[Blatman]

Which is why I think it may be getting an earth from somewhere, and yes it could be a short to earth from a break in the brown/yellow wire, or it could be that the lamp has been mistakenly wired to earth. He wouldn't be the first person to wire the ignition light to earth instead of the alternator...

[Sam]

Should i try to replace the brown and yellow wire completely to see if it works?

[Peter M]

What you could do is to disconnect the brown /yellow wire from the ign light and run a temporary wire from the ign light to the d+ terminal of the alternator and see if this works.The brown/yellow wire goes to the alternator via a 6 pin plug in the engine bay before going to the alternator.

As said in previous posts if the ignition light is lit with ignition on but with the brown/yellow wire disconnected from alternator then this could be the prob due to a short.

[Sam]

I will check this out Peter thank you.