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Electrical Problem. Bad earth?


paul richards

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When my sidelights are on the high level LED brake light (connected to nearside using Caterham sub loom) glows. Meter shows that there is 6.7 volts in the brake light wiring.

Most likely to be a bad earth. I've checked the earth on the wiper motor frame and all is OK. Are there any earths in the sidelight/brake light loom and if so where are they located?

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IIRC from when this was explained to me (here on BlatChat) you should be able to localise this by removing other bulbs one at a time and then chasing earths from the one that's doing this.

Another approach would be to add jumper leads from your other light units to a good earth then ditto.

Have you got the wiring diagram for your car? If you'd like one please send me a Private Mail with your email address.

Jonathan

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There is an Earth on one of the rear wing attachment bolts on my 1996 car - definitely on the LHS can't remember if there is one on the right. Mine is a small ring connector that attaches to the inside skin of the chassis using one of the through bolts, probably the 2nd bolt on the rear side of the wing. 

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Spent several frustrating hours at Paul's today.

Symptoms as above, both rear light units disconnected both seem OK, front lights disconnected and again all seems well, fuse pulled from brake light circuit yet still 6.7v going to brake lights with side lights on.

With side lights on and ignition off pressing brake pedal switches off the rear lights but not the fronts.  wiring checked along the rear chassis rail no damage or chafing.

Both stumped.

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Symptoms as above, both rear light units disconnected both seem OK, front lights disconnected and again all seems well, fuse pulled from brake light circuit yet still 6.7v going to brake lights with side lights on.

What is the effect on the behaviour of the high level brake light of disconnecting the rear lamp units at the connector near the units?

Jonathan 

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Had the problem where the tail and indicator bulbs flash alternately, the kind of thing you often see when following a French car.  The earth wire between the lamp unit and its connector was corroded along its entire length, I replaced the wire along with the earth pin in both sides of the connector.  The other side looked just as bad but hadn't started misbehaving yet.

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  • 2 weeks later...
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No progress I'm afraid. Various tests undertaken and no success. Currently no time to spare. Fortunately car is functional with only sympton being a slight glow on high level brake light when sidelights on. 

I'll try and find time in a couple of weeks. 

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  • 3 weeks later...
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After much trial, I finally sought the services of a mobile auto electrician who carried out similar tests and he was equally baffled. We were just coming to the conclusion that there must be a problem with the wiring and having checked it all except under the dash I was envisaging having to remove the scuttle to get at it all. We finally made one last check and removing the offside led rear stop tail bulb cut the 6.7 volts going to the brake circuit. Replaced the bulb and and hey presto all working fine. 

Couldn't believe that a bulb could go faulty like that and be responsible for such a failure.

Happy boy now *biggrin*. Now off to celebrate St. Pats day with a drop of Guinness.

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