928Myles

1990 S4 RHD - ex japan.

A couple of years ago after a couple of hours driving with the headlights on I lost the main lights (both dip & full). I ordered a replacement relay which fixed the problem. The problem started with a slow response to switching between low & high beam and ended in a 'hard' failure.

I was driving the same road a couple of nights ago and I started to have a slow response to switching to high beam. After a while I lost the high beam on both main lights. Everything worked as it should the next morning.

With the switch in the dip position all lights were on as normal (fog & main dip).
With the switch in the high position the fog, main dip & auxiliary (driving lights) were all on (but no main high beam).
With the switch pulled to 'flash' the lights the main high beam & driving lights were on and the fog & main dip off (as it should be for full beam).

It would seem to me to be a heat related problem (this time) as the problem went away when everything cooled down. Given that the symptoms are the same as when I had to replace the relay I want to know where to look before I have to replace another one!

My thoughts are:
If it is a fault in the relay why would everything work when the switch is pulled?
If it is a fault in the switch why would the driving lights come on and ALL the other lights also remain on?

Grounds are regularly cleaned.
All bulbs are factory wattages.

Any suggestions how to fix this would be most welcome.

Thanks,
Myles

FLYVMO

Myles,

I had a similar problem in my '86.5, it turned out to be the turn/cruise/washer/high-beam combination switch. It would flash high beams when pulled, but no high beams when pushed forward. Switching it out (before I knew about Deoxit...) solved the problem. I never had the issue of losing both low and high beams though...

Cheers!
Carl

928Myles

Thanks Carl.
It seems strange to me that I was able to get the driving lights to go without the main high beams going. I would have thought the same signal from the switch to tell the relay to operate both????

Will need to dig deeper into things when I get a chance.

Myles

545svk

I have the same issue, with mine appearing to be time or heat related.

My high beams work for around 5 minutes after switching on the lights, then I loose the main beams but keep the driving lights.

If I switch the lights on, select high beam and leave it on high, they stay on till I dip or switch them off.

So far I have changed globes, cleaned earths, checked wires and fuses, cleaned the relay connections and removed and cleaned the light switch and the flicker / bright switch.

Next is the ignition switch and relay,

I seldom drive at night and then not far so it's not a priority.

Alan

The additional high beams are driven by the turn/beam combo switch directly while the main headlights (high and low beams) go through the HL relay. This is partly so flash to pass always works on additional headlights (lights on or off).

Main candidates for different behaviour between these modes are: HL Relay, Combo switch, X-Bus from the Ignition Switch.

Alan

928Myles

I finally had a chance to check the relay (after another session losing high beam main lights).

All the contacts of the relay looked good (as they should - it is virtually brand new).
I put a small battery across the terminals of the relay that switches high beam for half an hour to imitate having the mains on for a period of time. Then I removed power then reapplied to emulate switching to low beam and then back to high.

The relay got reasonably hot but continued to switch correctly so I conclude that the problem must lie elsewhere......

Any tips for testing the X-bus from the ignition switch? (Alan)

Myles

the flyin' scotsman

have you taken the headlight covers off and inspect the bulb wiring/connector?

Dave928S

Might be time to get the multimeter out, to check for voltage drop with time, due to an increasingly resistive (with current flow/temperature) connection or switch.

Mrmerlin

spray all electric connections with deoxit including the switch

928Myles

Thanks for the replies folks.

Yes - all looks normal at that end.

That's the aim - looking for pointers on the best places to test. Due to the duration the lights are on before this happens the car will need to be running while I do this (which is against all the rules for electrical work).

The only Deoxit I have been able to source is a pen type applicator. Takes a bit more patience to use. Also says it should be wiped off after use........

Will keep hunting as I get the chance - too hot in the garage at the moment.

Cheers
Myles

928Myles

I cannot figure out from the wiring diagrams where the power to the headlight dimmer switch is sourced from nor where in the circuit fuse 5 (Auxiliary main beam) sits.

Can someone please advise?

I am off to dismantle the dimmer and light switches in order to get at them with DeOxit. No obvious overheating on any terminals visible without dismantling.

Cheers,
Myles

Alan

For the flash to pass mode (pull) the power is (30) for the high beam with headlights light on (pushed forward) it is (X).

You can test X (X-bus) in the fuse top test port (dimples on the body down to the terminals) for any fuse that is controlled by the X-Bus on a '90 these are Fuses 33-35 (check the CE panel page).

You cannot test a headlight relay without a proper test rig that allows many connections (30, 31, X, 30b, SM etc)

Alan

928Myles

Thanks Alan.
I cleaned the light switch & dimmer switches yesterday and ran the car with main beam on for 40min without a problem. The HL relay did get rather hot though (almost too hot to hold your hand against it).

I will investigate the power supply to the (X) bus and from there to the dimmer switch when I next get a chance.

Myles