Mike Frye

My guess would be aftermarket wiring somewhere. Some aftermarket alarms tap into the interior light circuit so that if anything is opened when the car is armed it will trigger the alarm.

Maybe something that you thought was completely isolated earlier (or didn't even know about) got shorted while you were driving to SITM?

I'm thinking the power for the alarm may have tapped off of a constant power line (maybe it's an inline fuse tapped straight off the battery?) and somehow that's now backfeeding through what had been the 'interior light' alarm input trigger.

Cosmo Kramer

Probably gonna do some more testing tonight, going to take Chris's advice and unplug E from the CE panel and see what happens. If the short to the clock disappears then I am going to pull the panel and check it for short circuits.

I have the factory alarm and nothing has ever been spliced in. I am one of the fortunate ones, the only part of my wiring that has been disturbed is the stereo.

Imo000

That's what my guess would be. The last thing you fixed was the window switch and the connector for it is in there. Something must have gotten disturbed when you were in there and then shorted out after the wires settled on the way to SITM.

Cosmo Kramer

I think something may have been off for a while, not just when I changed the switch. One anomaly on that circuit is the buzzer and seat belt warning. Since I have owned the car the seat belt light would illuminate periodically on its own and the chime would sound on occasion. When this short occurred the chime started going all the time, not full volume, just barely audible. I removed the chime module to keep it quiet. Not sure if they are related but just another clue!

I think my next step is to disconnect the battery and check for continuity to the clock power wire with an ohm meter on each side of every fuse to identify the circuit that is feeding it and go from there.

Whatever is causing this is not draining my battery of causing any other issues with how the car runs.

dcrasta

Check for crimped connections from aftermarket (Stereo) electrical work. If it's not soldered and heat-shrunk, its suspect wiring in my book. I have seen crimped wires detach, leaving a power wire or ground wire hanging and waiting to screw up your day..

Cosmo Kramer

OK finally got some time to work on this. Looks like I need to pull the CE panel as I have a short in behind it somewhere. I pulled plug E and checked the terminals on the CE panel. Terminals 11, 12 and 13 had a couple of stray volts going to them with fuse 24 pulled (fuse 24 feeds these three). Inserted a fuse into 24 (with plug E disconnected) and it blew instantly. Checked for continuity with an Ohm meter from un powered terminal on fuse 24 and only had continuity to terminal 11, 12 and 13 had huge resistance. Looks like I have to pull the panel.

Imo000

Or you can just wiggle the goard untill the short goes away! lol

Cosmo Kramer

OK pulled the CE. Everything looks good. Two wires from fuse 24, one goes to E13 terminal other feeds the noise suppressor relay and T11 terminal. Trying to figure out what T11 feeds, does anyone know?

Edit: OK just found it on the diagram T11 feeds the hatchback switch for the interior lights. Something has to be messed up back there.

Manfred

can't wait for the reveal.

Cosmo Kramer

OK panel back in. All wires good going to T11 and roof lights, no shorts that I can find!! So the only place left that could possibly be shorting is through the noise suppressor in relay spot XI. When I was checking for stray power to prongs E 11-13, when I hooked up my meter I initially saw 11.5 V. I left it connected and the numbers kept dropping until it got down to around .5V after about one minute. Could power going backwards through the suppressor cause this? BTW this was with fuse 24 pulled out so technically E 11-13 should have been dead.

According to the wiring diagram, terminal 31 off of the suppressor is linked to the trigger side of every relay in the panel. So a melted relay could be putting stray volts backwards through the suppressor, and to fuse 24 and terminals E 11-13.

Landseer

If I follow, that says you have shorts in the harness.

Imo000

Ted,

Did you touch the reat dome light before?

Cosmo Kramer

Imre: Wires to dome are good, checked continuity to T11/shorts to ground and the grounds wires are all good.

Chris: It has to be coming from the panel. When I unplug E connector to the panel the short to the clock disappears. I am getting abnormal voltage to E11-13 on the CE side and it can only come from T11 (dome light harness) or the suppressor socket.

Dmhager

I had the exact same symptoms listed on this post and thought that I would share what I found. Ill cut to the chase: resolving the shorts in the interior light (dome/door lamps/glove box lamp) and radio power circuits, plus a new fuse 24 resolved everything. In the case of my car (also an 85 US spec car), the PO had installed about every 80s yuppie accessory: aftermarket alarm, built in radar detector, radio and large amplifier (fortunately he didnt hack the speakers and speaker wiring) and the wiring was less than professional. As usual, returning the wiring to the original configuration that God and the Germans intended was all that was needed to make things work properly again. Just another example that its not 928s that have electrical gremlins, its the gremlins that are self-inflicted by inept owners and their hack accessory installation techs. Sadly, I encounter this all too often in my quest to save 928s for future generations.

There are a lot of potential circuits that can and are commonly shorted (either due to sloppy wiring or the commonly failed light switches overhead or in the door). I made a troubleshooting guide to help isolate the faults (using the factory wiring diagrams - definitely helpful to have them handy, but I always do better when I translate them to a troubleshooting sequence for the more complex circuits). It may not be perfect, and I am no electrical engineer, but it worked well enough for me. I do know how to turn on a volt-ohm meter, when to select Volts or Ohms and where to place the pointy bits. Here it is:

Beginning Symptoms (all not working):- Interior light

- Door lock lamp / red lights on door

- Hatch release

- Reverse lights

- PRNDL lights go off when the interior dome lights switched on

- Chime chiming all the time (faint in forward gears and a little louder in reverse) – pulled the chime relay for now

Key Circuits (for info):

Bus 30 is always hot (fed by battery through starter and alternator to top of CE panel). Bus 30 is the copper plate on top of the CE panel, with 3 4mm red wires bolted to with a 10mm nut / stud.

Fuse 24 feeds the following:

E11 – floor lamp left / door lock lamp (red); ignition switch (red/wht)

Note: ignition switch (red/black) then (blk/red) to H15 to U25 to backup light switch H2 and to Switch-X H23 (wire diagram C17)

E12 – floor lamp right / door lock lamp (red) –should read ~ 8 ohms with key off

E13 – 2 or 3 wires to clock, glove light, hatch unlocking and radio (wire diagram F5)

E13.1 – clock (wire diagram E3)

E13.2 - Glove box light splits at glove box light connect and goes to hatch unlocking right (wire diagram H17 and C5)

E13.3 – hatch unlocking left and radio (constant power) (wire diagram H17 and D45)

T11 – dome lights (interior and hatch 1 & 2) (wire diagram H8)



Troubleshooting Guide to find possible shorts in the above circuits:

1 – check for power at fuse 24, check for 12v at Bus 30 (should always be hot) and if good

Note: Bus 30 is fed by 3 red 4mm wires that connect to 1 10mm wire from the alternator. 1 10mm goes from the alternator to the starter then to the battery.

2 – check fuse 24 (mine was blown because of other shorts I fixed)

3 – pull plug E and check for short to ground at E11, E12, E13, T11 – if one or more has a short, then than is the problem(s)

4 – pull T plug and check T11 for short to ground


Backup Lights

6 pin connector at spare tire:

1 - Check bulbs first (for me, after resolving shorts in the interior lighting circuits, all I needed to do was replace my reverse light bulbs which were both bad), but if the bulbs are fine, keep going ...

2 – separate connector: check for continuity (on the switch side of the connector) between pins 5 (black/yellow/red) & 6 (grey/yellow) in reverse (open in park) - this confirms that the backup switch is working properly

3 - Pin 3 (brown) to ground – probe pin 3 and put the other probe on any ground to confirm switch ground.

4 - Check fuse (backup lights/mirror) and relay (XXII) - should have power at 30 with ignition, and 12v between 85 and 86 when in Reverse with ignition switch on.

If the above check out, then you may need to chase the wiring that runs to the back of the car.

One note, I never put the chime relay back in and everything works perfectly. Its possible that a defective chime relay contributed to some of my issues but I never bothered confirming because I prefer the sounds of silence until the motor starts.