Dome light always on

[bavareze66]

Hello!

Need ideas to solve the fact that the dome light in my 1988 Targa stays on in both ON and DOOR AJAR modes (but turns off in the central OFF position).

Even with both door jamb switches unscrewed and hanging, the wire that is supposed to be switched to GND remains always GND. And I assume there is a direct wire between the "switched GND" lamp connector and the two door jamb switches (installed in parallel). If that is right, then that wire is somewhere shorted to GND itself. But I might be wrong, if the circuit is more complex. My bentley manual shows no diagram for that. What would be the best approach?

Also, I found that bizarre part (3rd picture, labeled Stuttgart Connection, made in UK) piggybacked on top of the lamp. But I don't see it anywhere on the diagram. Is that an aftermarket thing, possibly to cut the light after being left on for too long to prevent battery drainage?

Thanks!

[ant7]

As you say, that box may be a delay for the interior light, try bypassing or removing it out of the circuit, as it may have become faulty.
The only other reason for the light staying on; is there must be a short to ground on the wire that the goes to either of the door switches, or somewhere leading to the interior lamp.
Ant.

[Correyyt]

The Stuttgart Connection thing you found piggybacked is definitely not factory. Porsche never fitted anything like that on a G-body car. You’re probably right that it’s an aftermarket “lamp saver” module those were sold in the ’90s and 2000s to shut off interior lights automatically after 10–15 minutes. If it’s failed, it could easily be backfeeding a permanent ground to your dome light.

[bavareze66]

Perhaps I did not explain very clearly.

I removed the circuit and then I did the troubleshooting, without it. As I said, I discovered that the switched GND is always grounded. Probably short to ground on the wire to the door jamb switches.

How is that wire routed? I want to disturb as few parts as possible while repairing the car. I had hoped this is a common problem and someone would point me to a presumed point of failure.

[ant7]

Using a test meter, if you haven't already done so; check each door switch to make sure they are not shorted, to do this, remove the wire from each switch directly, if both check out ie; they only connect when the plunger is fully out, then at least you have eliminated those as a posible issue, next, make sure there are no other connections to ground from each wire going to the switches, [this is all obvious stuff, but we need to establish where the short to ground is] if nothing shows up, then you will either have to pull the wiring up or down from the pillar, and check it, not sure what else I can suggest.

Update, just read that the wire going to the switches is still grounded without them being fixed to the door jam, so unfortunately your left with tracing the wire going to each switch, only way I can think of doing that is to pull the wiring up through where the light is, if you fix some new wire to each of the wires going to the switches, maybe you can pull the wiring up enough to find the issue, by fixing new [long] wires to where the switches fix, you should be able to pull the original cable back down without losing them somewhere in the door jam, hope this makes sense!
And if the wiring wont go up, try fixing some wire to the light end, and try pulling the cable down switch end [probably from the left side] to check it.
The fault may be where the cables join under the dash somewhere, or out in the frunk somewhere, check this first.
Ant.

[bavareze66]

Originally Posted by ant7

Update, just read that the wire going to the switches is still grounded without them being fixed to the door jam, so unfortunately your left with tracing the wire going to each switch, only way I can think of doing that is to pull the wiring up through where the light is, if you fix some new wire to each of the wires going to the switches, maybe you can pull the wiring up enough to find the issue, by fixing new [long] wires to where the switches fix, you should be able to pull the original cable back down without losing them somewhere in the door jam, hope this makes sense!
And if the wiring wont go up, try fixing some wire to the light end, and try pulling the cable down switch end [probably from the left side] to check it.
The fault may be where the cables join under the dash somewhere, or out in the frunk somewhere, check this first.
Ant.

Traced the wire behind the instrument cluster. Tried to pull down through the opening - seems stuck ,no move. Also pulled from the dome light side. Still no movement. Is there any other way to open the trim in such a way to figure out what's preventing it from moving?

[ant7]

Ok, can you trace where the wires for each door switch join together under the dash ?
Ant.

Originally Posted by bavareze66

Traced the wire behind the instrument cluster. Tried to pull down through the opening - seems stuck ,no move. Also pulled from the dome light side. Still no movement. Is there any other way to open the trim in such a way to figure out what's preventing it from moving?

[EC900]

Did this a while ago on coupe…that original dome
lamps don’t work is because housing clips are not contacting the roof frame because of headliner fabric. Keep that in mind - Ground is the metal
roof frame via the dome lamp housing clips. You’re getting power yet only dome rocker contacts are switching.

My guess is : Take a look at the connections on the housing as they may be incorrect or reversed when the old gadget was installed/removed. Your two hot wires may be on wrong housing spades.
Solid Brown attached to housing clip side spade completes switched ground when clip touches the body frame when snapped back in place.

Dont know if Targa has two domes. On coupes, wires are routed inside the pillars from main loom to driver side and then spade connected to passenger side and usually these get accidentally snagged.
No way to access pillar as these wires are fished.

Bad plunger spring can be making constant contact too - which in itself is a primitive gadget, wire twists when screwing it into the door frame causes wire to fray or breaks the switch and plunger not retracting enough, don’t recall if these have an adjustment, so look closely at the plunger action if it clears all the way around the switch housing enough to break the circuit as turn off lamp.

If you didn’t see this old post, explains the dimming gadget wiring…

https://forums.pelicanparts.com/porsche-911-technical-forum/171594-interior-light-delay-switch-print.html

[bavareze66]

Originally Posted by EC900

Dont know if Targa has two domes. On coupes, wires are routed inside the pillars from main loom to driver side and then spade connected to passenger side and usually these get accidentally snagged.
No way to access pillar as these wires are fished.


If you didn’t see this old post, explains the dimming gadget wiring…

https://forums.pelicanparts.com/porsche-911-technical-forum/171594-interior-light-delay-switch-print.html

As I said previously, I was able to narrow down this issue to the switched ground wire (going from the lamp to the door switch) being shorted to ground. The issue is not with the lamp or with the door jamb switches.

As such, I want to check the wire, make sure the insulation is still good. But I can't make the wire move through the pillar, it's stuck. Shall I pull harder? Or run another wire in parallel and leave the old one there disconnected?

I would prefer to maintain the car as original as possible, including the wiring.

[EC900]

Don’t yank, I believe the original loom is encased in a plastic sleeve along with other wires on circuit like glove box, trunk, clock and branches off and/or taped together.

Sure run some temporary wires and make connections if you want to see if there’s a break somewhere just to eliminate that probability.

Anyone can correct me if I’m wrong - but Brown White is the plunger wire and that is always Hot. Solid Brown is ground to the body.

If I get a chance I’ll pull my dome tomorrow. I can’t recall wiring or what I’ve done with mine when I fiddled with it.