I've got a Denso alternator, the one with a starter/battery terminal and two spade terminals (L & IG) as below:

I think my Sierra alternator switched the earth as the charging bulb on the instrument pod connected to the ignition feed (+12v) on one side and the old alternator via a blue wire (switched earth?) on the other.

When I connect the IG spade on the Denso alternator to an ignition (+12v) feed I don't get anything out of the L spade until I turn the ignition feed on at which point I then get the +12v out of the L spade.

I assume that I have to modify the sierra instrument PCB to take account of this by cutting the +12v ignition feed to the charging bulb out and putting an earth in its place?

If so, do I need a fuse in there somewhere?


[Edited on 20/5/08 by John.Taylor]
Rescued attachment Denso Wiring.gif

Or use a small relay to convert the new incoming +ve feed to a -ve one if you don't want to keep the Instrument PCB standard.

Use the incoming +ve to switch the coil of a relay and the main conacts of the relay for the -ve you require if you get what I mean.

Good idea on using the alternator live to switch an earth and I have a load of spare relays from the Sierra!!

I'm not sure if I understand your question but the charge light needs 2 live feeds (one each side) The bulb glows when the alternator switches to earth (ie not charging)

.... or have I misunderstood?

On my Denso alternator the ignition light wire is positive when the alternator is stationary and there is a supply to the other terminal [ignition on].

When the alternator is turning there is no supply to the ignition light and so it goes off.

However it is just a signal rather than a supply, so it won't power a normal bulb. It will light an LED or switch a low power relay though.

I've tried mine with a low power led and it works fine - I haven't reied it with the leds in my Acewell yet.

Stu