Ed Scherer

Yeah; this now sounds like a short in or at the bulb socket in the switch, which is likely caused by the bulb leads being crossed/shorted or the socket's contacts being shorted or perhaps foreign matter (and by that I don't mean German ) in the socket. I didn't consider that possibility. Sorry.

Luckily, that probably also means it'll be really easy to fix.

I can't remember. But AFAIK, every switch in the pod has just one connector.

Alan

There is an 86b terminal that is not used (this is normal).

The illumination of the LCD on the right is likely due to the loss of 1 or 2 of the 4 LCD illumination bulbs - there are separate bulbs (4) for the red warning mode - these are the same as the plain LCD illumination bulbs with little red rubber "condoms" on them - they do have a different order code. Interestingly I have seen these cheaper than the plain ones - since all you need to remove the condoms is an Xacto knife this is odd.

Alan

Ed Scherer

In case it's of use, here's the diagram for the defogger switch:



There are a number of tests you could do on the switch involving terminals 58, K, and 31. E.g.: resistance across K/31; will current flow from 58 to K (it should); will current flow from K to 58 (it shouldn't); etc.

If there's a short in the bulb socket or bulb contacts, you'd expect to see zero ohms (i.e., complete continuity) from terminal K to terminal 31. That's probably the best test to begin with. Ah... I just noticed that Alan already covered this in post #42. I'm doing too many things at once.

Ed Scherer

Regarding the info display backlighting, see my document Converting Porsche 928 Interior Lighting to LEDs for all sorts of information about getting into the cluster. It's a useful guide for the '89+ clusters, even if you're not converting to LEDs.

The bulb in question for you is the the rightmost one of the set of four red ones below (if you're talking about when the backlighting is red) or the one right above it (if you're talking about when the backlighting is amber):


(large version)



Note, though, that you don't need to go quite that far (as having the bulb PCB all the way out like I showed above) just to replace a bulb; you can do it from this point:


(large version)


Better view, with readable labels:


(large version)

Alan

If the dim segments are during just the normal illumination it will be one (or two) of the 4 plain bulbs Ed showed, the red bulbs are just for the red warning mode - but even so do provoke a warning to make sure they are OK too...

Remove a rear cluster bulb to provoke - easy...

I always wanted to try some other colors (the condoms are available in other colors - I actually have some in Orange, Yellow, Green and Blue) - and would like to test these for the 'normal' mode - however the orange is the 'natural' color of the LCD (the illumination light for this is just white) - so not sure how Blue for example would really work out...

I will try it one day... My pod has been super reliable for many years so no need yet...

Alan

Ed Scherer

I suspect that anything very far in the spectrum from orange/red wouldn't work out. That's a pretty strong orange filter they've got there.

Besides, relamping with LEDs is what you should probably do.


(large version)


(large version)

fonetico

Interesting that the remaining bit of collateral damage I had in all of this was the defroster switch.

I changed the bulb but it didn't light up unless I depressed it very gently. If I pushed it in all the way the dash lights would go out completely. The defroster seemed to be working though.

Gave up fiddling with it last week and coughed up the 30 bucks for a new switch. Everything working perfectly now.

Looking forward to the next challenge. Noises in my head are suggesting it just might be the front suspension. Is there ever any respite?

Manfred

Thanks Alan and Ed. Yeah, looks like I need to get the pod out again to change the bulbs. I'll get to testing the defroster switch tonight and report back. Things move slowly for me Monday through Friday...

Dan

Manfred

OK.

Resistance btw k and 31: 844ohms
Resistance btw k and 58: 908ohms
Resistance btw 31 and 58: 1.2ohms

Also, in doing the tests I noticed that the male connector at 31 is loose (it slides around in the plastic). I'm thinking it's time to replace the switch

Alan

58 -> 31 should be at least as much as 58 -> K - so I think a new switch is the right call here.

However the Rx values noted here are too high I think... probably the measurements method (esp w/ diode), doesn't change the appropriate action....

Alan

Manfred

I thought so too. I had to change the sensitivity range on my multimeter.


It was also very hard to get a stable read out on the 58 to 31--it was jumping all over the place but around 1.0-2.5 was where it seemed to spend most of it's time and at one point it settled on 1.2ohms so that's what I reported.

Manfred

Sad day. I got a new defroster switch from Roger and installed it and fuse 9 blew when I turned on the headlights (I had already buttoned up the rest of the pod including the potentiometer so I decided not to test the resistance of the circuit first). I had been happily driving around at night with the defroster switch disconnected and all my center console lights nicely on.

So, it appears the short is somewhere downstream of the defroster switch. I'll have to get the wiring diagrams out again and see if I can figure something out. At least the hunt is narrowed down somewhat.

Alan

Try taking out the defroster relay and putting the defroster switch back in... see what happens then?

Seems its related to the defroster switch still - the only thing that connects to the pod lighting in the defroster should be the bulb...

Alan

Manfred

No go. Fuse still blows with defroster relay out. I had a close look at the connector and the prongs on the inside are bent quite a bit but I can't see how it would cause a short.




Can the connector be replaced? It looks like I probably need to pull it apart and try testing resistance across the light bulb wires to see if there is still a short with the connector out of the picture.

Manfred

So, I'm still trying to figure this out. The wires feeding the defroster light come through connectors 58 (black/blue lead) and 31 (two brown leads) in the center where the contacts appear to be mangled. If I place a wire between connectors 58 and 31 my resistance drops to zero confirming a short. Does that mean the short is somewhere downstream of the connector or is that not helpful in localizing the short?

All wires go directly into a loom which then join a larger wire loom behind the pod so if the short is downstream it will be very tricky to find.

Does anyone know how to pull the wires out of the receptacle? If I could rig the wires to contact the switch directly without being in the receptacle and see if the short persists.