where would the earth wire be on a car headlight .?

Get a Haynes manual for your model of car, borrow one from the library if you can't afford one.

The electrical diagrams show the earth points as E numbers and list their locations.

Check for rust and tighten the terminal.

Edit

Using a tester can be misleading as an apparent earth will be found on a live terminal via the filament of the other headlamp as they are connected in parallel.

As has been suggested, you could check the wires and see if one of them is attached to the car body somewhere, if so, disconnect the wire, clean up where the wire attaches and then reattach. However, some bulbs earth where they fit into the bulb holder and do not have an earth wire. If this is the case, remove the bulb and use a bit of emery paper to clean the holder and bulb terminals.

Hi Kathy, the very easiest way to check for a earth connection is to go to your local auto shop & buy a circuit tester (bulb/lamp type), as soon as you have it connect the clamp end directly to the positive terminal on the battery and test the connecting plug to your headlight, checking each connector individually. as soon as you tester lights up then you have found your earth wire, check the wire color & trace it back to its connection on the bodywork

Good luck, hope this helps Leigh

hi cathy

well surprise surprise the metal body is the earth wire and a big one at that if it has any body left some just rot out around the lights so the last owner filled it with a plastic to make it look nice problem is plastic does not conduct electricity and the bulb looks dim so it might need a new wing on the car and a respray to make it look better.

good advice fromone of your replies. do no longer placed a 50 amp fuse as against a 30 amp. you will soften the wireing loom and the automobile would desire to bypass on hearth. fuses are there to guard by contrast. ok think ofyou've have been given a short circuit someplace interior the device. examine for water interior the rear lighting fixtures. examine the mild swap would desire to be defective, as would desire to the relay. If no luck, you will would desire to do a continuity try on the wireing. you are able to desire a multi meter for this. in case you would be unable to try this your self. a good automobile electrician will locate this fault very immediately.

For every vehicle every made? Or did you have a specific vehicle in mind? Absent that info, the only thing we can tell you is to follow the wires from the headlight socket and see where they attach to metal.