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post #4 of (permalink) Old 29th December 2006 Thread Starter
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Originally Posted by Horatio View Post
First of all, what are you using as the earth for your testing? It could be that it's being 'pulled up' when the voltage is applied to the system, and it's giving you a false reading. Ideally, you need the negative meter probe to be touching the car's chassis. Failing that, the outer shroud of the cigar lighter socket is usually a good substitute.

If it's still doing what you say, even with a known good ground, then it sounds like you have a high resistance on the wire between the F37 fuse and pin A3. This will give 12v when the circuit is not under load, but will drop much lower (possibly to zero) as soon as a load is applied.
OK with the resistor pack removed and my voltmeter across the A3 connector and a chassis earth stud I get 12V but as soon as I load it with a bulb (the one from the glove box) the voltage drops to zero. This is obviously the problem but what could possibly cause it?

I've checked the fuses under the bonnet next to the battery and they're all OK. The only other cause I can think of is that both wires in the loom that feed this supply have gone high resistance but that seems ridiculous.

Edit: Having looked a little more closely at the wiring loom, both the feed wires don't go as shown on the diagram, they go off to the driver's side of the dash and I'm wondering if they go via the ignition switch - anyone know?

Any more ideas?

Many thanks in advance.

Currently in wilbyforce's garage:
lot, walks and cycles sometimes but rarely runs.

Last edited by wilbyforce; 29th December 2006 at 12:58 PM.
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