Hi Alan

Search brought up this thread....

I have the same problem....

Main beam ONLY not working on passenger side (RHD CAR)

All others work fine including drivers side main beam....

I have changed the bulbs for new....still no main on left

I have changed the fuses for new....still no main on left

Arm was changed for new around 2 years ago....still no main on left

I am tempted to buy that huge relay which is so expensive but I changed it around 3 years ago when light were not rising correctly.....

So from reading this thread, do you think its a bad earth or broken wiring or should I buy the big relay again ?????

All the best Brett

 

Brett , i will add more info, if you take a look at the headlight harness where it feeds from the inner fenderwell then is secured by a metal tab this is the most likely place the wire has broken.
Thats going on the fact that the fuses are good.
The fender liner has to come out as well as the front block off plate then look at the harness it might be obvious

 

My brother S4 had a sillimar, where the passanger side low beam was half as bright. Turned out it was a bad ground and I splice another clean ground line into the harnes.

 

Hi

As the left main beam is OFF (NOT dim)

I would assume that both main and dip have the same earth, and as dip is working perfectly it should not be the earth ???

Which makes it the power ???

By the way on a 3 pin H4 bulb, does anyone know which pin is which ??

All the best Brett

 

Double check the wires at the bulb.

With the bulb removed and using a DVM set to dc volts put the black probe into the ground point of the bulb socket (brown wire) and with the headlight switch on probe the other bulb socket points with the red probe. You should read ~12v on the low beam (dip) point and same on high beam when switched. If the voltage reading is zero try moving the relevant wires to locate the problem.

 

I CERTAINLY isn't the HL relay if the other side works normally....

So don't waste the money.

Alan

 

I'm going to take a flyer in sailing speak and say loose connection at the headlight switch. Early on in my 928 career I had all sorts of light anomolies; even got pulled over for it. Turned out to be a loose connection.

 

Except its not at all likely for symptoms that affect only one side... since a single connector at the headlight switch feeds the relay that controls both sides...

Guys if you don't really understand how these systems work speculating randomly just creates additional often quite pointless work for someone to do...

For a single side malfunctioning - when the other side works correctly - the switch CANNOT be the culprit, nor can the relay. Its most likely a wiring issue in the final area where the pods rotating causes flexing in the wires. The only other possibilities are the bulbs, bulb holders, ground wiring (affects both lo/hi filaments) wiring back to the fuse, fuse, wiring back to the relay.

These are the ONLY options for the failure location. The most likely is at the pod/bulb end....

Alan

 

Hi

Just a quick update....

Got out my trusty Snap-On power probe and tested the left hand plug (under the cowl)

All ok apart from main beam power feed (white/black stripe)

No power there and if I feed power direct from the probe to the back of light then main beam works...

So at weekend its wheel off and arch cover off to start tracing the main power feed backwards...

All the best Brett

 

Brett...............you now need to do continuity tests pn the high beam wire and the connector.........there's a disconnect there somewhere.

 

Hi Malcom

Yes I know, but until I remove the arch shield and wheel I do not know where the next connector back is, unless you do ???

All the best Brett

 

Brett first place to look , is where the HL harness is clamped by the metal tab to the chassis it may also be in a black wire protector sheathing.
You will want to put the lights up to inspect the harness to see how much free play it has if its tight then thats most likely the broken wire spot.
Adding a bit of extra wire to the flex loop is a good thing.
i have found more than a few broken wires at this location.

Also look under the bottom of the headlight housing for the same condition

 

If by 'arch shield' you mean the headlamp cover then yes thats the first place to look...............couple of screws and you're there.

 

Hi

No that is where I tested...under the headlamp cover...

By arch shield I mean the plastic liner under the wing where I assume is the next connector to test continuity from ???


All the best Brett

 

There are no connectors in the wire harness between the relay panel and the headlamp, it is just one long loom.

I would suggest looking at the point that Mrmerlin has mentioned, this is where mine was broken as well. Follow the wires from the headlamp into the fender. Remove the wheel well liner and you are going to find the metal tab almost at the front bumper. Once you find the tab, you can open it and you will have enough slack to pull the wires into the headlamp recess to complete the repair. You will need to completely remove the headlamp and base to do the work.

I should have taken pics.

Michael