I respectfully disagree that his symptoms sound like a relay issue.

 

And, you may be right. Or, .....

 

Mike, if you go to Sheet 15 - Construction Components and look up Control Unit Instrument Light, it shows coordinates 7bQ for a LHD vehicle. You then look those up on the vehicle outline coordinates on the same sheet. In this case near the driver's side mirror and gas cap areas.

Relay 24 as mentioned above is the "Control Unit Instrument Light" module. It isn't shown as a "relay" on Sheet 1 - Lights.

Don't replace anything till you diagnose the problem.

 

I was going on the fact that the lights were intermittent, then quit. An energized relay, that is allegedly sticking, doesn't drop in and out. He then found a burnt fuse, which allowed them to come on. Now, there is a suspect dimmer, which doesn't work-a relay either energizes and conducts power, or it doesn't. A bad relay will not keep the dimmer from dimming. The dimmer seems like it is a possible culprit, or another related connection.

But, electrical gremlins ain't fun...so, it is hard to diagnose over the interwebs.

 

Ok...did some checking.

Fuse 36...good
R24 (license plate and instrument lights)...in place.

Ignition on, lights switch on. Gauges light up, but no dimmer control.

Fuse 36...taken out, lights off. Back in, lights on.
R24...taken out, lights off. Back in, lights on...still no dimmer control.

Looked at R12 (bridge)...don't have that relay.

Attached is a photo of my fuse and relay panel for reference.

Oh, also looked at fuse 18, but that only seems to affect gauge functionality only. No affect on the lights.

Just got a call from Porsche San Diego, new R24 relay is here. Will get it tomorrow and try it out.

Ok, will have to upload that photo later, can't seem to do it from my IPad.
Mike

 

Just read the rest of the post. Will look into the Construction Componants diagram and see what I can find. Will not replay relay until more trouble shooting is done.

Cheers,
Mike

 

Mike, it might be a good idea if you posted the model year of your 993.

This is the fuse and relay panel in my late 1995; no R24, but I have the R12 (bridge).

EDITED TO ADD: well there you go. Thats why it is important to list specifics. I just dragged out Vol VII of the Porsche Workshop Manual - Electrics, Wiring Diagrams and from 1996-on, R24 is in the fuse panel, which is why its not on my fuse panel. And re my PM to you, there are 4 sets of wiring diagrams: 95 (early 1995), 95/2 (late 1995), 96 and 97-98. BTW, the 96 and 97-98 schematics show a R12...go figure!

 

Alex,

I have a 97 993 Cab.
Classic red and tan w/black top.

I will post pictures of my fuse/relay box later. Wife is using the computer (homework) and I can't find a way to post pictures fom my IPad (maybe there's a Rennlist app for that...lol)

Going to Porsche San Diego to pick up new relay. Hopefully I won't need it, and will be able to return it. If not, maybe someone else will need it...

Will be back in a little bit.

Cheers
Mike

 

Ed may be right. My only experience is with my problem and fix. But I am hoping that swapping out the relay will fix your problem. It would be an easy fix!

 

Mike, with it looking like a solid state device I'm wondering how "bumps" can affect it other than maybe a bad solder joint on the circuit board.

Can you pop the cover off your old one and post pics. If the cover has a circuit printed on it, I'd like to see a pic of that as well. It doesn't even appear to be a "relay"; what would it be switching?

 

As promised here are the new photos.

1) is the cover from fuse box listing all the fuses and relays.
2) is a shot of the fuse panel. The "relay" in question is R24 located on the bottom row 3rd from right (its the black one with nothing on it; i.e. diagram or "1" sticker.
3) The "relay" in question.
4) The new "relay" (still in the box). The lable says "brightness control"...curious, maybe this isn't a traditional relay in the sence of "on/off"? It is the biggest one on the panel.

I don't know...

Cheers,
Mike
97 993 Cab

 

Alex,

I agree with you. Hence the reason I was thinking maybe a loose connector on the wiring harness...maybe in the dash behind the gauges. Thats really the only thing that make sense. Or, as I am wondering, is that relay, not really a relay as we are thinking, but actually a controller and its just mounted in fuse panel. Like maybe some kind of rheostat controled relay...?

As far as fuse 36 blowing that could be that I simply missed it, or my rooting around and wiggling wires "touched" the short with caused it to blow...?

Maybe my problem will be fixed by the new "relay", maybe not. Maybe the problem resides with the dimmer control's rheostat... Maybe the ash tray light has is playing a role. Previous owner had a Kenwood stereo installed (with amp under passenger seat) and an IPod cord routed through the ash tray (I like that actually, just plug the IPod in and stick it in the ash tray compartment).

About the old relay, are you saying I should try to pop the cover off, as in open it? Or were you meaning just to find a diagram on it. There is no diagram on the outside like many of the others, just what is in the photo.

Cheers,
Mike
97 993 Cab

 

Could be something more than a standard relay...as evidenced by the price?

 

I will admit I was a little surprised at the $114 price tag for a "relay". Luckily, however, if I don't install it, I can return it for a "restocking" fee...lol

 

You could always meet up with a Rennlist brethren in your area and borrow theirs to see if that is the problem. Quick plug and play and you'll know.