Electric Blues

[Herc]

It started out as a simple pre-MOT check on my '79 Elite. The car had an MOT 12 months ago, but hasn't been driven too much since, because I have been sorting out the interior. Prior to that, the car had been off the road for about 20 years, but in a dry garage. Dirty connections seem to be one of the consequences of the lay up.

All the lights were OK, including hazards, except the indicators weren't flashing, so I cleaned up the flasher contacts and it seemed OK.

The wipers and washers at the front were OK, but not the rear wiper. I knew that this had been a problem last year, and the guy who put it through the MOT had found a problem with a connection block of some sort. It sounds like a return of the same problem - I suspected this was the connections into the wiper motor, so I removed the wiper motor, and cleaned the contacts on that. I unwired the fuel pump so I could get better access to the connector block to the rear wiper motor. I cleaned this up as best I could and reassembled. No joy at all - the bottom-most fuse (well, 2nd to bottom but last isn't used) in the main fuse block by the brake servo (16amp) had blown. This seems to control all the wipers, indicators, but not hazards, nor front window lifts, nor main lights.

I have tried disconnecting everything, but I just can't stop blowing the fuse. I have disconnected the rear wiper motor, fuel pump, rear washer, heated rear window - no joy. I believe the cables run from the boot down alongside the driver seat and into a spagetti by the drivers feet. I have disconnected the cable loom coming from the back from the rest of the wiring, using the connector blocks down by the drivers feet. And STILL the fuse blows. Arghhhh!

My conclusion is that the problem is nothing to do with the rear end wiring at all. It might be something else I have fettled, or just giggled.

As you can deduce, I am not too familiar with debugging car electrics, so any ideas would be very welcome indeed.

Cheers

Herc

[matk]

At what point is it blowing? Start from beginnings, disconnect battery and check all fuses are intact. Then ignition off, reconnect the battery. Recheck all fuses, are they all OK? If so switch ignition to on without engine running, then recheck all fuses again. Start switching every electrical item on and off one at a time and check all fuses are intact at EVERY stage.

If you haven't blown a fuse yet then start turning items on and off in pairs. Continue experimenting untill you can tie down the exact time and combination of systems that blows the fuse. Until you can do this I can't see the point in just unplugging all your connectors, you need to establish the system or combination of systems that's blowing the fuse first.

[Herc]

Mat

The fuse blows as soon as I turn the ignition switch to the second position. At this point I believe have everything turned off that I can. Once the fuse has blown, what works and what doesn't seems to follow roughly the documented purpose of the blown fuse. Hence, I can wind the windows up and down.

When you turn to the second position, it enables a lot of things, as far as I can see - fuel pump, wipers etc.

Thanks

Herc.

[Wilf]

Unplug all accessories that use that fuse, and check with a multimeter that you do not have a short circuit - will confirm the loom is ok. Start plugging them back in one at a time and check for a short circuit each time. Its going to be cheaper on fuses!

[matk]

Yep agree.

If you don't have a multimeter, then similiar but it will cost you a fuse or two.

Turn ignition off completely. Unplug everything on that fuse circuit. Make sure all fuses are intact. Turn ignition on and check all fuses. Hopefully they are all still OK. Then plug back in each item one by one and check all fuses after each item. When it goes pop again, the last item you reconnected should be the culprit.

Good luck!!

[Herc]

Thanks for the input. It took a while, and when I found the culprit it was obviously where I should have started looking!

The cause of the fuse blowing was the three-position rear wiper switch on the centre console. I don't quite understand why it needs eight pins, but the insides seem to be recipe for shorting, by the look of things.

I should of guessed that the unconvincing action of the switch spelt trouble, but hindsight always has 20/20 vision.

Still, I am a tad more up to speed with the wiring diagram (more to follow shortly though!), and decidedly more expert at operating upside down, head first, in the drivers footwell.

Mark