Disco 1 Any Electrical Experts on Here?

My 1997 300tdi has a strange headlight issue.

The headlights do not work, neither on main beam or dip. Dim dip doesn't work either, but both sidelights are OK.
As soon as I turn the sidelights on the main-beam warning light comes on and stays on when I select main or dip beams..
Looking in the manual, the circuit diagram shows the main beam feed coming from the switch to both LH & RH bulbs and also to the warning light, whilst the dip-beams seem to be from a different circuit.
I suspect the switch is defective, but I would like someone who is more of an electrical expert than I am to give me an opinion.
Thanks in advance.

unplug the switch and make a bridge in the plug between the blue/white and brown/green wires( pins 3 - 5) see if you get main beam at the lamps and the warning then and if you do replace the switch, if not then it might become a nightmare (provided the bulbs are not blown)

Thanks for this.
The thing that seems most confusing is the fact that the main-beam warning is on all the time, not just on main-beam.
I guess I'll strip the switch out and check it all with my multi-meter.

The most confusing is that the warning is on and the lamps are not cos they are on the same feed.,..that's why i recommended that test cos it might be a short and a voltage drop within the switch which can bring on the warning but not stromg enough for the lamps.

I have a couple HNCs in mechanical & and electrical engineering but I don’t think that makes me an expert

The D1s electrical system is very straight forward, first of all unplug the dim-dip resistor and leave it unplugged as u don’t need the facility. So, if not all but most, of the issues that u have are with the lighting switch, so get a replacement and hopefully all should be good.
But of course test first

check all earths, then the switch

Sorry to jump in

I fitted the resistor and relay to get the dim dip function, just because it's useful to me, but am I rite in thinking that is known for causing problems as well

Towsey

When it cools down a bit I shall borrow a switch from a friend and try replacing it first, after testing the connectivity.

My first thought was the switch, but I thought I would ask you 'Disco Gurus' first.

Thanks for your adice and I'll let you know the result.

I finally got round to looking at the problem today. I've been busy doing my Mk.1 Mini Cooper 'S' of late so the Disco took a back seat, but was driveable so it was not a problem.

I stripped the switch out, but could see no issues. I got circuit integrity across the switch with 12 volt power to the headlight fuses. However, I was getting 12 volts to the two main-beam and the two dip-beam fuses all at the same time when I switched the headlights on.

Then I took the connector off of the LH headlight and the plastic connector looked in bad shape with corroded terminals. I cut the connector off and left the wires with no ends then tried the headlights and the RH headlight worked fine. I made up some new direct connectors for the 3 connections, lightly greased and re-connected them.

It all works fine now. The only thing is I still can't work out why the main-beam warning was coming on with the sidelight switch only. But it's all fine now.
Thank you all for your advice.

Cooperman1 said:

The only thing is I still can't work out why the main-beam warning was coming on with the sidelight switch only.

Click to expand...

That was fixed by itself when you dismantled the switch

Yes, I guess that is the case.