oldman40

anyone have a wiring diagram for a 1996 993tt?

specifically, i need interior and hood light connections to the alarm module, which i believe controls the open/close ground circuit to turn them on when the door or hood opens.

ive been sorting out some electrical issues with non-functioning alarm, double flashing door leds, and interior and hood lights that do not work when doors/hood opened.

i've made progress with the alarm function and now get the single flashes indicating proper arming (broken ground lead at the acm connector). however, lights still don't turn on with door/hood opening. the lights turn on fine when in the "always on" position, and the hood light has voltage, but no current, indicating either a faulty ground or open circuit at the alarm module. i favor the latter over the former due to the fact that both interior and hood lights appear to have a common ground switch at the acm.

also appreciate any advice from experienced RListers, thanks!

nine9six

Here is some info that may be helpful...

https://rennlist.com/forums/993-foru...zer-issue.html

Scrumpy

Yeah, come join the misery! Lots of good information so far. As far as an accurate full wiring diagram, I don't have one but I've heard alldata.com might be a good place to start. Depending on where you live, your library card might get you access as well (unfortunately mine does not).

oldman40

Misery is right, Porsche purgatory.

Thanks, signed up south all data, fyi found promo code RENEWDIY for a one year subscription of $9.95 or two year for $12.95.

Pretty comprehensive archives on my first glance. Will start delving into this some more...

oldman40

ok pardon the simple question, what is "terminal 41" on the wiring diagram??? that is a square box with the number 41 written inside of it. it appears to be a common connection point between the interior and hood lights enroute to the alarm module.

thanks in advance,

AllMine

http://www.928-electrics.com/wiring%...%20primers.htm

Great place to start for full comprehension of Porsche wiring diagrams.
Curt

oldman40

Thanks, I did read that already. Says it's a ground point, but I can't determine where gp 41 is located based on the wiring diagram. Thought also it might refer to a DIN classification but according to my research doesn't list 41 as one of the designations.

Found the ground point wiring diagram on alldata too but nothing labeled 41....

hoggel

Responded to your PM.

41 is a splice in the Passenger Compartment wiring loom.

The ground for the Luggage Compartment Light, and the Inside Lights (not RS) in the auto position, is through the Alarm Control Unit. In the PM I said it was Alarm CU plug II pin 7. The diagram below that I sketched a couple years ago says plug I. The diagram I have in front of me is fuzzy so I can't tell if it is plug I or II. I'll verify when I get home and can look at the diagram in the FRM.

What is not shown in the sketch below is that the door contacts will also turn on the lights through the Alarm CU. The Ignition Lock Light is also grounded through 41 to the Alarm CU.

oldman40

a big thanks to hoggel for keeping me on track thinking about this problem! in the chance that my tribulations might help someone down the line, i'll tell my story:

discovered that my interior lights (dome, hood) ground wire to the alarm control unit (acu) was bad, showing voltage and high resistance. so i tried a parallel ground wire from the interior light switch (br/ws wire) to the acu. please note that my alarm arms normally with single flashes when i normally lock the car. also, the door switches and hood microswitches are working in that the door buzzer sounds when i've got the key in ignition and open either door or the hood.

here's where it get weird. with the new ground wire in place:

1. if the doors are locked, and the lights are off, then the fob DOES turn on the lights.
2. if the doors are unlocked, and the lights are on, nothing will turn off the lights, not the fob, key in ignition (in position 0, 1, or 2), nor opening/closing doors.
3. if the doors are unlocked and i open the door or hood, the lights will NOT turn on.

to me this could indicate: 1. the ground to the acu from the door switches is bad, or 2. an acu relay between the door switch ground and the interior lights is stuck in the off position. neither of these explains why the fob can turn on the lights, but not turn it off.

i checked my door switches: no problems and again it seemed to work just fine with the door buzzer. So i checked my grounds to the ACU at pins I/7 and II/21 (door switch contacts). when i grounded the I/7 pin (interior lights), the interior lights turned on! but they wouldn't turn off no matter what i did with the fob or doors or ignition.

SO, i figured i had a bad relay in the ACU and bought a new ACU online. Well i plugged it in with fingers crossed, and.....Nothing. same problem.

Frustrated, I started digging into the interior lights ground wire starting at the ACU then working backwards along the taped up passenger compartment wiring loom. About 10 inches aways from the ACU, i noticed that there was a bunch of solder points and heat shrink, indicating that perhaps a prior aftermarket alarm was removed and put back to stock.

then i started thinking some more, and figured that nothing was turning the lights out because the acu is not seeing the ground disconnect from the door switches. i thought perhaps the 2 br/ws ground wires were accidentally switched by the prior installer.

so i took a chance at switching the ground wires I/7 and II/21 and VOILA!

all is working perfectly. i absolutely hate electrical gremlins, but i'm glad i hadn't started pulling out the entire wiring loom before figuring this out.

i can only hope that down the road anyone with prior-owner installs and this problem might find my weird one-off situation helpful.

hoggel

Nice fix! Those 'previously modified' circuits can cause some crazy problems.