What have I missed? non Zed electrical problem - SORTED

[Crazy Harry]

So I spent all day trying to sort this and now my brain is melting.

My 1995 Caterham is due its MOT on Friday and when I checked it over a few days ago everything was fine except that the O/S side light; tail light and the dash lights don't come on.

All three use the same fuse. The fuse is OK and when the switch is pressed there is 10 volts at the fuse but nothing at the bulbs. The earths for the light clusters are good and in any case they are shared by headlight; indicators and stop light which all work.

I have removed and replaced about 400mm of loom to the rear light cluster which was a 'dogs dinner' of old connectors and repairs so all good there. Even when new the loom in a Caterham is a bit of a 'mare with quite a few connectors not used. Nothing under the dash or in the engine bay that looks like the two ends should be together. Checked the loom under the car - no cuts etc.

I have replaced the speedo and throttle cables in the last week but nothing looks disturbed. The battery could do with a charge but lights the same lights on the N/S and the brake/fog lights. Given voltage at the fuse and nothing at the bulb holders is this a power drain? one bad bulb wouldn't cause this would it?

So apart from charging the battery and starting again what am I missing here? What should I check next?

[Crazy Harry]

This may help some of you other 'classic car' lads who I know are also Zed owners.

So having charged the battery over night I started again this morning. Neither of the two Caterham reference sheets I have for the fuse box look anything like the arrangement in my car. Some fuse pulling later and I was able to identify which fuse did what. I found that the fuse for the side; tail and dash lights had blown - replaced it and it blew again.

Given I had worked on the speedo I started there. Pulled the bulbs from the back of it - no problem with the bulbs except that about 2mm of the metal bulb side wall was showing past the plastic holder. When fitted into the speedo head this bare metal must have been in contact with the metal of the speedo casing and shorted out. Solution was not pushing the holders in all the way!

All in it took around a day and a half to find it - lucky it was my time not garage time! ..... and just the MOT at the end of the week now

[ph001]

Nice find. Problems like that can be a real bitch to isolate.