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Earthing Problem

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I have a weird electrical problem that I think is due to a bad earth somewhere.

Basically all electrics work fine until I use the headlights, when the headlights are on - be it dip, main and full beam the rest of the electrical systems are effected - the wipers slow, the heater slows and when I flash the lights the radio dies.

Clearly (correct me if I'm wrong here) I have an earth problem on the headlights, question is where is the earth connection for the headlights?


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Earths for the wing lights are ringed in red...

post-20087-071339000 1285761734_thumb.jpg

I find it quite intruging, earth problems, the main effect is due to how the actual loom is put together, you regulalry find several earth terminals joining to one wire which then is attached to the body somewhere (its also usually wrapped in black tape so you can'r find it easily. The net effect is you start getting a voltage "earthing" into other systems, then the potential different decreeses causing circuits to have problems functioning, if its an old vehicle, then the main earth for the lights is in the wings. s the lights, apart from starter motor are a pretty big draw on current, but I'd be suprised that it could have such a large net effect over the whole system... just an amature butchers comments, maybe fridge can add some of his know how...?

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Not necessarily a fault with the headlight earth wiring specifically.

It depends what year car it is, they are wired up differently depending on age/generation.

Some (most?) are wired with the main battery earth from battery to chassis and then linked to the engine block, but if it's wired from battery to engine and then to body, the starter will fire up OK but if the connection from engine to chassis/body is loose/dirty/corroded then you could get the symptoms described.

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..... remembering that the headlights get mildly brighter with the hand brake on ...

That could be a bit of a give-away then, sounds like the engine to body earth is coming through the brake cable and any other vague connection it can find.

I remember having similar problems with a old Mini many years ago where the throttle & choke cables used to smoke on starting the engine :lol:

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