Blitz993

Hi,

My car's instrument lights stopped working and I think I've got a short somewhere in the 58d circuit - the dimmed instrument light signal. I'd like to start isolating different parts of that circuit and, by process of elimination, find the short.

My question is about the schematic symbol which is a square box with a number in it. I believe these correlate to physical terminal or crimp connections where one wire comes in (58d in this case) and then gets distributed to several destinations. If I could find that junction, designated as box 2 on my 1995 Porsche 911 Schematic, sheet 1, I'd be very happy. I've had a long look behind the instruments in the dash - you could be looking straight at it and not realize what you're looking at. Cramped space with awkward access and dark.

Does anyone have any tips on how to find where this junction might be?

hoggel

There is a location illustration toward the back of the wiring diagrams.

Cupcar

The box with the "2" in it is an internal splice in the wiring harness "Wire Loom Passenger Compartment". If you were to unwrap the harness you would find a waterproof connector with all those wires bundled.

Note the "Box 2" is located in coordinate field "N3" (corresponds to numbers and letters surrounding sheet 1) and there is a green wire with a blue stripe (GN/BL) going from that to a vertical row of boxes starting at top with "G53" in it for example. This is a coordinate where the wire goes to on another page of the wiring sheets.

In your wiring diagrams go to find "G53" which is in Page 6 "Instruments and Sensors", looking in that field you will find a box with "58d N3" which refers to the coordinate field you started with on sheet one and it goes to the speedometer at pin #7.

The rest of the fields in the vertical row can be traced is similar fashion.

Blitz993

@cupcar - Thank you, that is what I am after. The waterproof connector is useful information - I haven 't needed to find one of those square-box junctions until now. Finding the short will probably be easier than finding this junction unless there's a nice way to expose the space behind the dash for better access!

@hoggel, I don't think the square box symbols appear in the location charts towards the back of the schematic sheets all I can see there are connectors, ground points and construction components.

Thank you both for taking the time to reply.

ToreB

The junctions might also be soldered, covered by a shrink tube, bundled within the wiring loom covering.
I have never seen references to their exact positions in the loom.
Cheers,
Tore

Cupcar

Exactly, what I meant by a waterproof connection. Searching for the junctions is hard, sometimes they can be felt in the loom - but then when you cut into the loom, you find the junction is not the one you wanted!

BTW, the OEM tape used to wrap the harness is almost exactly like the tape here in the USA that is sold for hockey sticks in athletic equipment stores.

IXLR8

Are you talking about your instrument light alone or all lights in the switches, ashtray as well. That 2 in the box feeds many things.

Because if it is the instruments alone, then I would check what voltage you are getting to them (as well as grounds) and then work backwards.

Blitz993

Hi IXLR8,

It's the whole circuit, pretty sure it's a short that's why I wanted to find the junction so I could isolate parts of the wiring and see if the short goes away.

BTW - @cupcar (or anyone) you referenced that stack of implicit connections at sheet 1, coordinate N3. There must also be an undocumented junction somehow related to that stack; the schematic makes it look like 1 wire is distributed to all the instruments (Sheet 6) and some other destinations on Sheet 3. There must be either a single wire with taps along its length or, better still, another undocumented junction.

Experimentation will answer that, I guess.

IXLR8

Do you have power to pin 7 of the Instrument Light Control Unit when the light switch is on in any of the positions except off?

Do you have ground at pin 5 of the Instrument Light Control Unit?

Also, rotate the Instrument Light Potentiometer and measure at pin 2 of the Instrument Light Control Unit.

If the above checks out OK, then you would have power at pin 4 (58d) of the Instrument Light Control Unit. If not, then the unit is faulty.

Lets start there.

Fuses all check out OK?

Cupcar

My bet is the "real" wiring diagram is the tooling they used to layout and produce a harness and there were some deviations from the paper plan.

IXLR8

Rory,

Doing a search on RL, I see that you have tried to tackle this problem earlier in the summer on this thread.

From reading parts of that thread, I see you jumpered the ILCU relay and all lights came on. So why do you think there is an issue at the splitter 2 in the square box?
If you think you have a short, meter it out to confirm.

If you bought a new relay (R24 is it?) as you claimed you did, then the issue is either a ground for the ILCU or the potentiometer controlling it.

I came across a good one while doing a search. Imagine someone posted "Are the lights in series and you may've broken a wire when you did the speedo?" I had to chuckle about the "lights in series part" these aren't Christmas Tree lights.

Hey, you have a Cardinal. I checked out a few people on them.

Blitz993

Yes, and I was so sure I'd found the problem I even made a movie of the procedure.

The root cause was not the ILCU as I originally thought - after driving about 3 kliks with the jumper replacing the ILCU all the lights went off and stayed off. I measured the resistance between pin 4 and ground and got a very low number like 0.04 ohms IIRC. Another RL member helped me out and measured 1 ohm on his car. I pulled out 9 instrument lights and the resistance didn't change - should have increased.

Actually, the original relay started working after my messing around but I assumed it was flakey and decided to take a chance on a new one. The symptoms were exactly the same, the lights came on briefly and then went out, plus the backlight on the trip computer stopped working entirely when the ILCU was installed. Now I have 2 relays and tomorrow will take them to work to test with a scope. My friend also scoped his outputs and now I have a known good specimen to compare against.

You never know - I won't rule it out, my cigar lighter didn't light up (when they were still working, a month ago :-( ), neither does the headlight control ****. Process of elimination is my main tool and I wanted to pull all the lamps from the switches, instruments and center console and see if the "short" went away. Haven't figured out how to get at the console and the control ***** then started eyeing that #2 junction thinking I could start isolating parts of the circuit from there. The electrical part would be easy-ish if everything was more accessible

Yeah - although it's slower and less powerful than the 911


Thanks to all for your interest and suggestions - if I ever figure it out I'll post an update

Cheers!