IXLR8

Mike, I doubt the Control Unit would be loose in the fuse panel socket unless someone has removed it a hundred times in the past. Anything plugged into the fuse panel is usually very tight to remove.

If it is the Control Unit, and since you stated that your instrument lights went on and off while hitting bumps, then I might assume a bad solder joint on the circuit board within the Control Unit. You might give it a couple of good hits and check what your instrument lights are doing while parked in a dark garage.

If the Control Unit is assembled like the DME relay for example, then the cover can be removed. And if the same crappy soldering techniques are used on the Control Unit as on the DME relay, then I'd suspect a bad solder joint.

IXLR8

I doubt it is a relay. As mentioned before, the Porsche wiring diagrams shows a transistor symbol, ie solid state.

If there is any "switching" they may be varying the on/off pulse width electronically to vary the instrument light intensity.

I would have pulled mine out to have a look at it, but unlike yours, it is stuck in behind the instrument panel.

As Chuck mentioned, I'd find a local 993 owner and switch Control Units if you want to be able to return the one you bought...just in case.

IXLR8

Mike, that is easy enough to check. You can check this by connecting a DMM to the following pins in the R24 socket in the fuse panel. If the DMM meter probes don't fit, use some paper clips. Actually, an analogue meter is best for this purpose.

P2 - P3 is across the resistor of the dimmer control. That should be a fixed resistance of unknown value.

P1 is the wiper.

P1 - P2: as you turn the **** Clockwise, the resistance should increase or decrease.
P1 - P3: should do the opposite of P1 - P2.

usnlynx

Alex,

Haven't been able to test the relay sockets yet (hope to do that tomorrow), but I have done some minor surgery on the R24 "relay". See the interesting pictures...

1) is the inside of the "relay"
2) is the circuit board.

Looks like someone has done some surgery previously, note the red circles. There is a blob of some kind of resin on the top left (inside) and again on the circuit board (red circle area). Also, you can see that the base is chewed up, appearing to show it has been opened before.

BTY, this doesn't look like any relay that I am familiar with. I could be wrong, but I am thinking this is not a relay, but a controler.

IXLR8

Mike, what you can do is pull the "controller" and drive around with 58 and 58d jumpered. Make a short jumper by crimping two male push-on connectors onto a piece of wire. If the instrument panel lights stay on without going intermittent over bumps, you've narrowed it down to the "controller" or the dimmer control.

If true, I'd check that dimmer control first and if OK, you can go with that new overpriced controller ($114 for $2 worth of components ), or you can re-solder all connections on the original controller and see if that does the trick. I'd clean off the varnish first before re-soldering.

BTW, that L9611B chip is a PWM Power MOS Controller chip which makes sense for this application of varying the pulse width to control brightness. You might want to check the component connected to the heat sink.

Isn't this fun...it beats Sudoku puzzles.

deuce1

Are there any updates to this?? I am in the same situation right now and am not having any luck getting my dash lights to work and was wondering if this new VDO controller module fixed the issue?

pp000830

If you are speaking of a key way light to help illuminate the ignition key hole I am not sure such a feature was available on the 993.
My car did not have one and I added it.
Look to see if a previous owner added it and may have caused a wire failure where it is tapped into the dome light or dash light circuit.

Andy

Sword_of_the_Spirit

I know some have had issues with dash lights and have probably stumbled across this and other threads. I will lend some insight since having a similar issue that was resolved with a slightly different fix.

Last Summer I notice after going over a bump (of all things), my dashlights flickered and eventually went completely out. I reset the interior/exterior 3P light controller and that seemed to get things back to normal. I figured it was not serious and did not put any thought into the problem after returning home.

Flash forward a couple of months.

After starting the car one early morning, my dashlights did not appear. Everything (all exterior) was working as normal (as mentioned prior, little thought/research was put toward this issue). Needing to get to my destination, I used my cell to glance at the speedo to gather a bearing on my speed. On the way, I tried to reset the interior/exterior lights with the 3P controller without luck. So I research and stumble upon this and one other thread regarding the dash light issue. To my chagrine, the ash tray light is burnt out and one of the tail lights is out. I promptly replace those items as it seems electrical resistance can play a part. Wallah, my lights are finally working after repeated misfortune (for a week) and it is nigh on winter storage.

With April 2013 fast approaching, I'm doing my dilligence to the 993 in its upkeep. In doing so, my dash lights do not turn on as previously noted. Confused, I start operating any "light" controller (while car is off and ignition key removed) in a fashion to replicate use. Nothing is working until I get the dashlight dimmer. I've found desktop radios that are left at a specific volume will display irregular decibels when operated either higher/lower. By replicating a couple of days use, the radio works fine. In much the same way the radio volume controler needs regular use, so I found with the light dimmer. I spent about 2min operating the dimmer in various postions. I can report I have had no issue since.

As such, I strongly believe some of these little electrical devices need periodic use (I personally drive very seldom at night). In addition, periodic inspection of bulbs that burnt out need replacing since the issue is may be finicky to electrical resistance. The same is said of the A/C system when only driven on that "special" day. It will need use to operate effectively. Sir Isaac (Newton) had something to say about this.......

Hope this helps,

Michael

TRM

Michael, I was also going to suggest he checks the ash tray light. I had taken mine out and simply connected the two wires to complete the circuit. But by doing that it totally messed up the dash lights and they wouldn't come on at all. Very weird! As soon as I spliced the ashtray lamp back in - poof! Working dash lights.

Not sure if this may somehow help with the dimmer however.

pp000830

Does a blown fuse suggest too big a load or a short to ground?
I believe you describe a light that illuminates the ignition keyhole on dash earlier in this thread.
I believe no such light existed from the factory. I would pull out one a gauge and check the wiring to this light as any aftermarket added light may suffer from poor wiring or a shorted element.
Ay :-)

Blitz993

I am still chasing the problem on my '95 993 and this thread has a lot of good information in it - but it really helps to have read the schematics, identified the instrument light control unit (ILCU) by sight, etc.

My situation is the same as this thread - the lights got intermittent originally, then stopped working completely. The intermittent operation was not because of going over a bump, but the car was moving and they are vibrational machines.

First of all, there is no fuse protecting the dashboard lights, as far as I can tell from reading the schematics. The lights are powered by terminal 30 (Battery +). You can trace a line directly from the battery terminal to the ILCU without ever going through a fuse. I wonder if the ILCU has built-in protection circuitry - great photos of the unit by usnlynx, above - thanks for posting those.

Fuse 36 protects the license plate lights - easy to verify from the schematics.

Fuse 18 provides power to the instruments from circuit 15 (battery + with ignition turned on). That means it protects the instruments which require power to work - not the instrument lights. Fuse 18 is a red herring.

In my case I was convinced the problem was the ILCU, bought another one, and ... same problem. The lights actually started working, but then went out again. Switching off momentarily then on again fixed it ... briefly.

The reason I thought it was the ILCU was because jumpering terminal 58 (instrument lights amongst others) to terminal 58d actually worked and the lights came on and stayed on. When the brand new ILCU stopped working I decided to try another experiment - install the jumper and go for a longer ride. If the lights stayed on in that case, my next move would have been to check the dimmer rheostat. I had already done this, BTW, noting that it didn't match the pin descriptions on the schematic. I connected everything together on the work bench, varied the rheostat and expected to see voltage variation on terminal 58d. I did see some, but only about 0.5 volts worth which I thought was surprising. But that was with the original ILCU, so maybe it was defective.

Anyhow, I took the car for a drive with the jumper installed. Great - lights on at full intensity. And then - nothing. They went off and stayed off - jumper had not worked loose, in fact it got welded into the socket.

Someone above posted some very good advice - Don't replace anything until you diagnose the problem". Even my attempts to diagnose it have landed me in deeper doodoo. Next steps will be to clear the socket of the jumper wire, then go hunting _downstream_ (toward all the instrument lights) for a short or something.

JTBuffmire

I went through a very similar issue recently. Turns out it was my Headlight Switch. The fact that my license plate lights were also out (they're on the same circuit), was the convincing straw. Fortunately, I was able to purchase one on Amazon for $139 and have it installed for 0.5 hrs of labor at a local shop (which around San Francisco is still ~$100). Porsche part# 996 613 535 00. Picture below.

Fixed the issue!

Chuck W.

The headlight switch can cause a number of problems on the 996 and 986 Porsche. I believe that is the switch you have posted here. The 993 headlight part number is 993 613 353 100 and a completely different part. It would be nice if the 993 headlight switch was responsible for these issues.