Pesky ignition light

[Richard_M]

I'd driving me nuts.

TR8 (original). Ignition light does not go off when running.
Alternator? Tried that - had it checked and all's good.
Checked a wiring diagram (TR7) and the circuit seems simple - the small wire from the alternator goes direct to the ignition light bulb and either provides an earth or doesn't.
Earth when stopped, something near 12v when running. As the bulb has 12v on the other end of it it is either on or off.
I do electrics, but am no expert on alternators. The wiring between alternator and lamp is good. If I take the wires off the alternator and put an earth on the smaller one,  the lamp goes on and off.

To me, it HAS to be a fault with the alternator, but it's been off to be checked twice and last time it had its diode pack changed.

Any ideas?

Thx

[trekcarbonboy]

You didn't put an LED in there did you? I did and had a similar problem. Put the bulb back in and no problem.
Thats my only thought, since I know nothing about the electrics.