993 alarm control unit and interior lights woes

[oldman40]

hi all, 

 

first time post here, thanks in advance for any advice, especially loren!

 

i've got a 1996 993tt with interior lights that did not turn on when hood or doors opened.  i discovered that my ground wire to the alarm control unit (acu) was bad.  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.

 

does this look like a bad acu module? if so, is it repairable?  also note that my acu p/n is 928618260-02, which represents the early generation of the acu's, later superseded by p/n xxxxxxxxx-03

 

thanks,

Edited January 21, 2016 by oldman40