FredR

Have had a problem recently in that the headlights will not raise/lower. The problem initially dissappeared after a day or two and then re-appeared never to reset itself a few weeks ago.

The lights work OK after manually cranking the lifter mechanism. The fuse [27?] is OK [93 GTS Euro spec wiring] so I guess it is either the relay or the light switch [do these things ever fail?] itself that is shot.

Just getting round to dealing with it before the heat returns and could not identify the relay involved. A wild guess [the wiring diagram] tells me it may be the double size one in the bottom right corner [relay xx111/xx1v]- can anyone kindly confirm this relay is used to trigger the electric actuator and how best to diagnose what is wrong other than swapping out this relay.

Is there an easy way to test the motor is spinning without removing it? Looks a bit tricky to get in there. Clearly I need to eliminate the obvious here.

Regards

fred

WallyP

Temporarily deleted - more study needed!

Alan

Its somewhat unlikely to be the light switch (low power connection & switches seem reliable), it could be the motor itself, the motor mounted limit switches or the relay - yes the big expensive XXIII/XXIV.

Don't buy parts until you deduce what it is. There are various config of relay and motor by year - make sure you only get the right ones when you know what you need, switches are all the same.

#27 is the headlight motor fuse - check it (not by looking at it or replacing it) test it with an ohmmeter/continuity tester.

You can test the headlight motor directly by unplugging it and on the motor side plug apply power and ground to pins 1 & 5 - use a fused source (15A). In one polarity it goes up and in the other down. Pin 1 has the Red/Black wire on the car side while Pin 5 has the Black/Blue wire on the car side.

To test the limit switches connect a continuity tester/DMM ohmmeter between pins 3 & 4 and 2 & 4 on the HL motor. With the HL all the way down - I believe IIRC that you will see no continuity between 4 & 2 until you start to raise the lights - then you will have continuity all the way to the top. With the HL all the way up - you will have no continuity between 3 & 4 until you start lowering the lights then you will have continuity all the way to the bottom. (NB I may have the pairs descriptions reversed here - if so thats OK).

I'm not sure what the motor connector wire colors are but Pin 2 = Brown/Red (on car side), Pin 3 = White/Black (on car side) and Pin 4 = Brown (on car side)

To test the HL switch (for this issue) - Remove the HL relay. Based on the labelling on the relay can
test the relay socket connector with a DMM on volts mode - make up some leads with crimped on male 0.25" blade/spade connectors (Ace HW or similar). Connect to a good ground - you can just use pin 31 on the relay socket.

With ignition on you should see 12v+ at pin 86M - only when the light switch is in position 2 (HL on). Pin 30b should have 12v+ only when the light switch is in position 0 (all lights off).

If the motor and both switches seem OK I think its a HL relay problem, you could open it up and check if the contacts are stuck - there are 4 relays in there. Usually the motor drive part is very reliable though. Overall I'd say the motor mounted limit switches are the most likely culprits here... you may want to start there after verifying the fuse.

Alan

dzaprev

I bet its headlight relay . Sounds exactly like what happen to me .

Alan

Yes possible - but lets do some testing first...

Alan

WallyP

Fred,

I'm afraid that we both are in for an educational experience...

When you are relaxed, and have some time to concentrate, go to Page 97-429.

The shaded box in the lower center is the combo headlamp relay - Relay XXIII-XXIV. There are four single-pole, double-throw relays and an electronic box inside the combo relay.

The two end relays power the headlamp motor/gearbox to raise and lower the headlamps. The relays apply power and earth to the two motor leads, and reverse the power and earth to reverse the motor.

Find Fuse 27 and follow the circuit to the combo relay. (If you don't mind marking up your manual, or can make a copy of the page, highlighters make this a lot easier.) The power flows to Terminal 30a, and then to one of the disconnected contacts on each of the end relays. These contacts are the input power for the headlamp motor.

The shaded box on the far left of the page represents the headlamp motor. Follow the power/earth leads from the motor to the combo relay, where they connect to the top of the slanted lines in the end relays. This slanted line connecting the dots in the relays represents the movable contact arm, which is operated by the relay coil, which is the rectangle with the slash.

The other end of the contact arm is connected to the second contact in each of the end relays. If you follow the circuit from each of these contacts, you will see that they are connected to GP V, so are permanently earthed. This means that at rest, each of the motor leads are earthed, so the motor doesn't run.

When the coil of either of the two end relays is powered and earthed, the contact arm on that relay flips from the earthed contact to the power contact, and the motor runs. The direction that the motor runs depends upon which relay operates.

Now it gets interesting. Assume that the headlamp switch and/or the electronic box in the relay apply power to one side of the relay coils. Follow the circuit from the upper connection on the relay coil of the relay on the left end of the combo over to the headlamp motor/gearbox.

The circuit goes to Terminal 3, and then to the line going to the odd shape. This odd shape represents a copper disk with cut-away segments that is mounted on the output shaft of the gearbox. The output shaft drives the arm that rotates the headlamp bar. The three horizontal lines represent copper wipers that drag on the copper disk and the insulating segments at the cut-away areas.

Note that the center wiper circuit goes to Terminal 4, then down to GP 1, where it is permanently earthed. When the top wiper is on the copper, that circuit is earthed. This means that the left relay coil will be energized, the relay arm will flip to the other contact, and the motor will now have power on one side (from the power contact of the right relay) and earth on the other (from the now-earthed contact of the left relay), and so the motor will run.

The motor will run until the copper disk rotates counterclockwise enough that the wiper is off the copper and on the insulating segment of the disk.

So, your problem can be:
- No power from Fuse 27 to the contacts on the end relays.
- No earth from GP V to the contacts on the end relays.
- No power from the headlamp switch to the combo relay.
- Faulty combo relay.
- Faulty contact between the wipers and the copper disk (wear, hardened grease, dirt).
- A faulty connection or broken wire at any point in the circuit you just traced.

First test: remove the combo relay and test for battery voltage on Terminal 30a in the socket. No power shows a problem with Fuse 27 or its connections.

Next: Turn ignition switch and the headlamp switch on and test for battery voltage on Terminal 30b in the socket. No power shows a problem with the headlamp switch or a connection.

Next: Install the combo relay. With the ignition switch on and the headlamp switch on, remove the rubber cover and rotate the manual raising ****. Stay clear of the linkage and headlamps! If the headlamps suddenly rise, the problem is likely to be faulty contact between the copper disk and the wipers.

Further testing might require inserting short strands of wire into each of the five terminals on the motor/gearbox connector, ensuring that they do not touch each other, but that they stick out enough to allow you to check the circuits for power and earth while all are fully connected and powered.

Good luck, my friend...

dzaprev

Wally P thats what I am talking about !

FredR

Wally, Alan etc,

Many thanks for the guidance/thoughs here. After 5 years of trouble free motoring since putting this 928 on the road I have had little to no problems other than a/c gas leaking so not a bad run.

In the last few weeks I seem to have been jumping from minor issue to minor issue not to mention my Daimler Century falling to pieces- time for at least one new vehicle of some kind I suspect!

Of course the 928 is still gonig to get pampered- just hope I can get to the bottom of the problem before the heat returns in about a month or so. I should have a spare relay in my box of spare parts from the 90 S4 assuming they may be one and the same. Why the bugger they had to spec such a complicated relay in one box I......-never mind - it's a Porsche ffs.

Hopefully I can get to the bottom of hte problem this weekend with those useful analyitical tips and if all else fails- get the local dealers to take a crack at it.

Regards/many thanks

Fred

Mrmerlin

dont be afraid to open the relay,
look at the wires and the relay contacts inside it,
sometimes the small wires break that run around the relay coils,
and or a bad solder joint or a corroded relay contact

FredR

Stan,

If it's mechanically possible to fix then I reckon I have a good shout at fixing it. Also, we have some very good back street shops run by artisan's from the Asian sub continent who can also work wonders.

I was looking through my parts bins to see if I could find the relay from my late S4 1990 circuit board -could not fnd it but the wiring diagram suggests they are configured differently- whether such could be made to work -no idea.

Plenty to go on here thanks to everyone- another weekend in the car port-hopefully I ca sort this before the chaps from Dubai arrive!

Regards

Fred

Alan

Fred - there are some minor changes between late model years in secondary functions (park-up for wash) but they are all generally compatible and should work. That is any S4 & later relay should work in any other S4 and later. So if you can find the '90 relay give it a try.

Pre-S4 cars have a completely different relay and motor and are not compatible.

The very earliest cars have a different scheme again and don't even have the double relay.

Alan

FredR

Alan,
Thanks for the tip- kind of figured that may be the case by my knowledge of electronics is dodgy at best. I should have the part but you know how it is- you keep a pile of crap for years and then you cannot find the bit you need!

Regards

Fred

Dictys

Fred, you can try my relay in your car on Friday as my car is a 1990 S4

FredR

Hopefully I will have it worked out before you guys arrive. I'd hate to try soemthing and then you end up in the lurch with no lights at all! At least I can operate them by manually liting them- just a PITA!

I have also had a bit of aproblem recently with battery drain- now starting to wonder if the two problems are inter-connected.

Regards

Fred

Mrmerlin

if your having a battery drain then shut off the car let it sit for 20 mins,
then go open the CE panel and with your IR gun,
shoot the relays, any one thats hotter than the rest may be sticking,
remove it and open the relay