Strange headlight issue SOLVED

Hi all, gen 3 Jimny, my left headlamp is very dim, right is fine, but when I take out the right hand bulb, the left goes out - as if they're wired in series! That can't be, surely, so any other thoughts before I start digging into the wiring? Nb, we also have a battery drain, possibly connected?

Sounds like you are on right track looking at the wires, could be a bad connection or something has been rubbing or worse eaten by vermin.

This normally happens if one of the lights has lost it's earth, and one light earths through the other.

HOWEVER

For some reason that I can't quite fathom, the headlights on a jimny use a common live, and switch the earths!

So at a guess the live feed for the left headlight has failed, and a filament is in series with the filament in the Right headlight that is supposed to be off.


Check the live feed to the left headlight (White/red) which comes through it's own fuse - number 7 on my diagram.

You might find that it is shorted to earth and blown the fuse, check for screws going into the wiring harness or the wire stuck on a sharp edge.
It could even be internal to the bulb, the main beam filament has gone dead short and blew the fuse when you went to main beam.

Not your issue, but the headlights were always dim on my gen 3, and thinking about your problem, only 6 years after I sold it, it occurs to me that the one thing I never checked was if previous owner had fitted uprated bulbs, which will always end up dimmer than standard as the thin wires cannot supply the extra current.
It would only have taken a few minutes to just fit new standard bulbs as a check too!

A degraded live to the LH lamp is what I'm thinking, because that could be the source of our drain too. Will inestigate tomorrow.

A bad connection or partially burnt out cable will give a dim headlamp, but won’t, in itself, cause a battery drain. If a bad connection is causing a reduced current when switched on, it won’t cause any drain when off.

It’s possible that both problems are connected, although equally possible that you have two faults. If you have a chaffed wire (live), it might be making a partial connection to chassis and causing both a current drain and poor headlight, but it’s more likely to blow the fuse as too much current would be drawn in a short. It’s possible a cable has shorted out, partially burnt out a cable, blown the fuse, which has then been replaced, this might give a reduced current drain in a short circuit situation.

Is the Jimny new to you and/or has this just started happening, this might help track the problem down, especially if it started after fitting something new?

Other items which cause a current drain are aftermarket accessories, often a stereo and especially an Android head unit that hasn’t been wired correctly.

Robin