Headlight fault

240GL 1989 SAL. Both dip & main beam, both sides have stopped working. All other lights function normally. When lighting switch is operated a relay can be heard on moving from park to head position. Headlmp flash on indicator stalk does nothing, nor does main beam warning light illuminate. Fuse is OK. (no. 5 8A). I have a haynes manual, and an enlarged wiring diagram but cannot seem to make any sense of it?? Can anyone advise where to begin, apart from an auto electrician !!! Thanks..

[cbyard]

This might help a bit or not(?) but if the circuit for 1989 doesn't make much sense, try looking at one of the earlier ones in the Haynes book. Haynes is mostly USA model oriented and they seemed to get electrics and especially fuel injection systems etc updated much earlier than UK models.

Since nothing works it does sound like a feed side problem rather than earthing or bulbs. Relays can fail and still make clicking noises so if you locate any relays in the headlamp circuit it's worth checking both sides of each contact circuit for voltage, and check at each side of the fuse when fitted as well.

Can't offer more now as I haven't got Haynes here at present.

Good Luck

Chris

Thanks Chris..earlier diagrams look pretty much the same. This evening I found another relay under the bonnet near the battery which operates when beam (stalk) switch is moved. Next to this I found 2 other relays behind power steering reservoir, which appear to be linked to pair fog lamps and pair spot lamps. From one of these was a wire burned which enters harness!!! I think the accessory lamps have overloaded somewhere and possibly damaged a relay. The problem is identifying which relay is which (step...what does that do?) main, bulb fail etc etc.. I am on the verge of buying a couple of relays and installing a complete replacement circuit for headlamps. Haynes is practically useless as the legend is so poorly printed it is illegible. Identifying connector numbers and wire colours is ok in places, but with huge gaps. I would possibly fare better with a proper diagram. Any thoughts on where I may acquire one?

[cbyard]

Hi Bob

the "step relay" converts the operation of the dip/main beam stalk which is "intermittent" (ie it returns to its original position as soon as you let go, unlike most cars where there are distinct dip and main positions) into the two steady states for dip or main. It "steps" alternately from one state to the other each time it is pulsed by the dip switch. Don't know exactly how it works, mine does so I've never had to investigate. I could give you chapter, verse and circuit diagram for the famous fuel pump relay but that's another story!

Burnt wiring sounds unpleasant- it could be due either to overloading or more likely since it should be fairly conservatively rated (most car systems are more concerned with voltage drops than limiting current ratings for cables) there will be mechanical damage or a bad connection nearby- perhaps a failing contact in a relay socket or inside the relay itself. This might well have caused collateral damage (nice euphemistic military term, that) to your headlamp circuit.

Running low on any specific advice here- I'm not really familiar with the headlamp circuit itself. Afraid I haven't got anything better than Haynes myself though I think there was a recent reference by someone in this forum to having something called a "green book" which sounded like some genuine Volvo document.

Chris

Thanks Chris. After some serious disassembly I have removed spotlamps & foglamps and all associated wiring, relays and switches. Following your advice to look at earlier years things began to look a little clearer. I also cut the harness open along the inner wing to find the extent of burned cable. Didn't have to go far till I found main beam (LH) loops back and into 'step relay' near battery. I removed this and after close examination found that the base was partially melted, allowing contact to 'fall over!'. This locked the rocker in one position, not in contact with either circuit... SO tomorrow I am going to get a replacement step relay, and some new cable etc. and hopefully all will be well. The fault I believe originated in Spotlamp which was wired direct into LH main beam supply side. I am an electronics engineer by trade so this has been so frustrating. However I think I now understand how the whole thing works except for what is in the bulb failure unit. This appears to be an integral part of the dip beam circuit. I am probably now in a position to help others with this type of problem, it having kept me awake at night for some days.. Thanks for your good advice. The earlier diagram was the clincher.

Bob.

Chris,
The bulb failure relay operates by passing the current from say, the left and right headlamps through two separate coils either side of a reed switch, which, if the current is equal in both coils is held in it`s normally open position, an imbalace of current in the coils causes the reed switch to be pulled one way or the other lighting the warning light. These systems are very over sensitive and can even be triggered by bulbs from different manufactures taking slightly different currents.
A lot of people avoid this problem by removing the bulb from the dash light!
A somewhat ignominious end for a bulb failure warning system!
Colin.

[cbyard]

Hi Bob

sounds like you did a good job, there!

Snap re jobs- hope I didn't sound too waffly or talk downish about the relay and dipswitch!

Interested in a description of the innards of the step relay if you pulled it open (what do I mean IF?!)..... and thanks Colin for describing the bulb failure unit- that's a pain if you fit trailer wiring 'cos there's only one brake light feed to a trailer. Still the little orange light reminds you something's hanging on the back!

All the best

Chris :-)