Driving Light Problem

[kevroe]

Any ideas on what to check next with this one please. Driving light passenger side doesn't work. Drivers side does. I have 12v DC across the lamp terminals which drops to zero when I touch the terminals so the lamp should light. I've changed the bulb but I'm mystified what to check next. Current is clearly there but disappears when the circuit is made. Someone will probably say 'bad earth' but where would this be and why do all the other circuits work?

Any thoughts
Kev

[jimed]

I'm fairly sure the wiring with connectors goes round near the bonnet hinges; this leaves them open to all sorts of stuff thrown up from the road and was the cause of all the front lighting issues I had with my S. There may be 12v there but if the connectors round the hinges are really corroded there may not be enough wumph to actually light the light - so well worth checking all the connectors round the bonnet hinges (where there are inner wings fitted to the bonnet they are behind those but easy to get to with 2 nuts/bolts each side). You may well find the wire is a bit worse for wear each side of the connector and have to work round that.
Jim

[MnS]

Earth problems can show in weird ways, check wiring loom from that side and strip back the insulating tape,mines an S2 so no driving lights but the connectors were in that part of the loom, there may be some there not so good as Jim says. The wiring runs by the radiator and the manifolds so heat could affect it. I had a problem recently, all fine with nearside indicators when no lights on, but turn the lights on and the indicators doubled in pace and the front nearside one wouldnt work, turn full beam on and the nearside headlight would dim only getting 4V at terminals. I ran a new earth in from the chassis point under the washer reservoir to the headlight wiring, all good now for mine. Good luck

Ian

[v8s4me]

Based on a similar experience, the connector blocks mentioned above would be where I’d start.

[Ragtop]

That’s an interesting post Kevin. Here are a few suggestions.

1. When you say ‘touch the terminals’, if you mean touch them together that’s not really a good idea. If you didn’t have a poor connection you would end up with a blown fuse, or worse.

2. It’s voltage that is ‘clearly there’, not current. If you put the bulb in place then measure the voltage across the bulb terminals, I expect you will find very little voltage because you have a high resistance elsewhere which is ‘choking’ the circuit.

3. The ‘high resistance’ is likely to be in a connector, or possibly in the bulbholder itself. The fact that the problem is limited to one arm of the wiring circuit should make it easy to track down.

HTH – G.