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

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