Bad earth - one dipped beam goes out when main beam engaged

Hi,

Just took the mk1 in for an MOT, failed one things

1) when changing from dipped beam to main beam, the offside dipped beam bulb goes out (the near side one stays on) - the tester said a faulty earth?

basically. how do I go about testing if my cars has a faulty earth, where should i check?


any help would be great.

thanks

will

I'm pretty sure that the dipped beam 'should' go out when you put on full beam

sounds like a fuse or wiring fault to me, best way to check is with a multimeter and haynes manual

I have this issue too, its not an earth, but its a dodgy connection at the back of the fusebox. I think its a large yellow wire which goes to the headlamp, although on mine its the nearside full beam which doesn't come on. So your might be the other colour, (red I think, but not sure here…) I think you'd have to trace it back from the lamp to the fusebox….

Mine was doing the same and I've started going through the fuse box (old style) replacing all the fuses with new ones and rubbing down contacts with emery paper (to remove corrosion), the headlights now works fine.  I still cannot get my n/s side lights to work (front and rear) and one indicator flashes very fast.  I have discovered that water has been getting to the back of the fuse box and I think this has caused a bad earth. maybe the same has happened to yours?

if it's the internal's of the fusebox that's gone and your's is an early type non-GTI

I have an old stock new fusebox in original box  8)

thanks for all the help every one,

I attacked the problem last night and after wiggling earths, replacing fuses and bulbs the problem seemed to sort itself.

I love my mk1.

cheers

Have a look at MateyMatey's website.  They list a mod for the headlamp wiring that bypasses the fusebox and wires the headlamps straight across the battery (via a relay and fuses of course!).  The upshot of this is that you get 12V across the bulbs not 10.5 or 11V, and the lights are sooo much brighter  8) .  It uses the feed from the fusebox to control the relay, so if you have only one side working you could control it with that.  The important thing is that you can use some good thick wire to run the power, say, 14AWG, not the tiny wire that is fitted as standard.

Managed to track down my problem to a bad earth on the boot floor, after cleaning up the rosettes under the dash etc.  Now the rear indicator has stopped working and cant get the fog light to work