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Interior Dome Lights

 
Old 02-14-2019, 09:12 AM
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cbeiswenger
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Angry Interior Dome Lights

I'm hoping someone can help me. I have a 1986.5 928S and the interior lights are driving me crazy. The door lights come on and off when you open/close the doors as normal. However, the dome lights will not (both front and rear). I can get them to come on manually by clicking them on, but when put into the position to come on/off with the doors they won't work. Any suggestions??
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Old 02-14-2019, 10:20 AM
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Wisconsin Joe
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The lights have constant power to them.
There's a constant ground, so that you can switch them on & off manually.
There's a switched ground going to the door & hatch switches so they can come on when you open a door.

From your description, the switches work. There's hot to them, there's constant ground to them. The switched ground is bad.

Helpful hint: If you spend waaaaay too much time on here, you will know that this issue comes up every so often. Like a couple days ago:


https://rennlist.com/forums/928-foru...or-lights.html

Diagrams, pics and advice from some people who know their schtuff.
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Old 02-14-2019, 10:26 AM
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What's got me confused is that the door lights work properly. It seems that if the switched ground was bad none of them would work or am I not understanding this....I'm not an electrician for sure!
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Old 02-14-2019, 10:48 AM
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I am working through a similar issue and will be posting a detailed thread soon. In the meantime, there is a path from your door switches to the overhead interior lights. They are actually on a parallel circuit to the door lights but are separated (I guess so if one fails the other still works).

The door controlled grounding of the light circuit is accomplished by a brown/white wire. The part of the circuit that controls the overheads originates at connector U, pin 2 on the CE Panel. It is alongside a red wire at U1. The circuit is designed such that the lights have power all the time (through fuse 23) and the light actually turns on when the door switch grounds the circuit (door is open). The two wires run in the harness that runs along the body below the passenger door and turns up just behind the door in the b-pillar. There is a 6 pin connector at the B-pillar. At this point, the circuit splits (two wires to each pin) and one set of wires runs through a black set of wires up and into the hatch, the other set of cables travels up the B-pillar into the roof, attached to the body just above the door, and across to the front light.

So - the front light and rear light are on a 'sub-circuit' of sorts. At the rear light over the back seats, there is another piggyback cable that runs down the passenger side of the hatch lid and connects the hatch light into the circuit.

NOTE: (I feel like Stan - wish I knew as much)...the wires to the front light (at least on my '83) are the same colors as the diagram and the wires at the CE panel: red (+12v), brown/wht (door grounding), brown (grounding for the on/off portion of the switch). At the 6-pin in the B-pillar, black wires are used to carry the circuit up to the hatch. For the extension to the rear hatch light, the colors change again to White, green and brown.

It sounds to me like you have an issue in the brown/wht part of the circuit, since your lights will manually operate. They are getting power (red wire is good) and they are grounded for manual operation. I would (battery disconnected) start testing for continuity between the different parts of the circuit (U2 at the CE panel to the 6 pin at the B-pillar, 6 pin at B-pillar to front light, etc. to isolate the issue.

Since NONE of your overheads work with the door open, I suspect the issue lies somewhere between the pin switches and U2 on the CE Panel, or between the CE panel U2 and the first 6-pin connector.

I'll rework some of this and add some pics I have been taking along the way so we have a writeup of how the system works and what everything looks like and where it is located.

Hope this helps.

-scott
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Old 02-14-2019, 10:49 AM
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Wisconsin Joe
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Read the linked thread.

He had a similar problem. Door lights worked, Uppers didn't.

The wiring branches off.
I will guess that your switched ground is bad after the split.

If you plan on doing your own work, you will need to know electrical stuff. It's not all that hard. Basic, high school level, shop class electrical knowledge will take care of most of the car just fine.

Try some of this:
https://www.google.com/search?ei=in9lXMSsGoictAW5kq-oDQ&q=automotive+electrical+basics+101&oq=automotive+electrical+basics+1 01&gs_l=psy-ab.3...36720.39311..39944...0.0..0.186.1454.1j10......0....1..gws-wiz.......0i71j0i13j0i8i13i30j0i8i13i10i30.zBVCkJb4124

Edit to add:

Scott posted his reply while I was composing mine.
He is the one who started the thread I linked.
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Old 02-14-2019, 12:08 PM
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Thank you both (Wisconsin Joe & drscottsmith) for your replies and help! I feel like I'm way further ahead on tackling this issue! Appreciate the help.
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Old 02-14-2019, 07:15 PM
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just for a WAG please post a picture of how the over head lamps are currently wired,
its quite possible to put the wires on the wrong lead.
NOTE every lamp must be wired the same way
that means the power wire must be on the correct post as well as the switched wire,
the ground wire goes to the frame of the lamp.

Last edited by Mrmerlin; 02-14-2019 at 07:55 PM.
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