I'm so stupid... Was: Head Cleaners

From: Rob O'Donnell <classiccmp.org_at_irrelevant.fsnet.co.uk>
Date: Fri Jul 2 02:07:23 2004

At 23:09 01/07/2004, Tony Duell wrote:

>Two other car electrical faults that have caught me...


I had an interesting one on our old car (Vauxhall Cavalier). I suddenly
had a couple of warning lights come on. The battery charge light, and I
think another one. The odd thing was, they were operating in inverse to
normal - usually when switching on, the battery light would show until the
engine started, then go out. It was staying off until this point, then
coming on.

We had one of those haynes service manuals (it was an old car, so we'd
bought it just in case) and after poring over the virtually indecipherable
schematics, I traced the current flow for this lamp. (From memory:) this
lamp was nominally connected between +ve and the output of the
alternator. This when the alternator was charging, there was no potential
difference, so the lamp stayed off. However, if the fuse in the +ve supply
blew, it could to draw current /backwards,/ via a different circuit on the
same fuse, from the ground line... thus causing the lamp to light when
there was charge, instead of the reverse.

I checked the fuse, and it had indeed blown. replaced it, and all was OK
again!

A weird design.. and horrible schematics ...

Rob
Received on Fri Jul 02 2004 - 02:07:23 BST