LoneShark

Howdy, all. Next item on my lengthy chore list for the 87 S4 auto is to get the Hatch Release working. So far I've repaired and/or verified operation of the driver/passenger switches and aft contact switch, and measured the following at the motor harness connector:
Red = 12 volts always (same at Q25)
Yellow = 11 volts when "switched" (same at E13)
Brown = 11 volts always

At the contact swith connector I see:
Brown = Gnd
Br & Br/Wht = 11 volts always

So... grounding issue in the Brown wires? Am I missing some subtlety of the operations logic? The ground point VI near the spare tire seems to be fine. Doors open or closed doesn't seem to matter. Suggestions on where to to check the harness w/out ripping the car and harness apart?

In event anyone notices a root cause, here are some other items on the to-do list:
Missing Interior Lights relay
Stop Light warning light
Loose Tensioner warning light (I've verified belt tension OK a couple of times)
etc. etc. etc.

Thanks!

Mrmerlin

stop light might be the center light in the window,
take it out and clean it make sure its the same as the bulbs in the lights
the hatch motor may need a new diode. (This if the motor wont stop after a cycle indicates a bad diode)
but you didnt explain what it is doing when the switch is pulled if it wont work at all then check the fuses and check the harness where it plugs into the motor

jon928se

Br WHt at 11v with the doors shut would be about right - what you are actually measuring is +12v from the battery through the interior lights acting as a bit of resistance. This doesn't really tell you anything but that the interior light switches on the doors work. BrWht is the switched earth from the interior lights through the door switches to ground. Hatch release won't work without the doors open and Br Wht connected to ground.

Can't recall what Yellow does but as there is a transistor inside the hatch release motor the 11v you measure on Yellow could just be +12v going through the transistor without a ground.

Alan

The brown on the motor (brown/white later years) should be grounded when either door is open - if it is not you will never be able to initiate an unlock cycle.

Yellow goes to ~12v when switch is pulled and Brown must be at ground due to door open for the circuit to start. Once started the red wire can continue the cycle operation until the park posistion is reached. The red wire is supplied by the 1A fuse on the CE panel.

Alan

LoneShark

Thanks for the ideas and observations. Here's a status:

- Red wire OK (12V always)

- Yellow wire OK (11V when switched)

- Ground wire definitely messed-up (11V regardless of doors open/closed)

- Motor & Circuit Board - I have no idea of condition, as it has never moved or made a peep for me. If anyone has a circuit diagram handy, or can suggest continuity/resistance checks at what pins, I'd appreciate it. Else I'll search tonight.

- 3rd brake light? What 3rd brake light? Just realized my little project has none. I wonder if that could be causing the ground issue...?

borland

Hatch release motor circuit diagram and repair link...

https://rennlist.com/forums/928-foru...ase-motor.html

Mrmerlin

the 86 and newer cars have a 3rd brake light inside the top of the hatch window,
2 screws, one on either side of the housing remove it

LoneShark

Tonight's Update: (Man I'm investing a lot of time on this one task)

My '87 project car is definitely missing the third brakelight, I see now were it should be attached along with two snipped wire stubs.

I was wrong about the Yellow hatch release wire providing proper voltage. Apparently I was reading the 11V from the shorted ground wire that was passing thru the motor board and back out the yellow wire from the "inside out". Fixed this by replacing a... fuse (sigh). Now I have a solid 12V at Yellow when the switch is pulled.

Now motor will turn (for first time yeah!), and will continue to turn as long as the release **** is pulled. It does stop turning when I release the switch. It does not "park". I'm not sure if this is the same symptom described in borland's link, as it refers to runnning continuously until the connector is removed (mine only runs as long as the switch is engaged).

Is this proper operation?

borland

If you take a look at the hatch release motor repair thread, you'll see a photo of a gear that has a slip ring with a short break or gap in it.

That slip ring is connected to the constant +12V. The motor runs with constant +12V (red wire) until it encounters the gap in the slip ring, at which point the motor loses power and stops.

The Yellow wire from the pull switch provides another source of +12V power to get the motor running again, far enough across the gap in the slip ring. Again the motor runs until it encounter the gap and looses power and stops.

So, based on what you've described, it appears to be that the Red wire (constant +12V) is not connected to the slip ring inside the motor or the motor is not connected to the slip ring.

The repair thread fixed a motor with a defective brake circuit, where the motor would simply coast past the gap in the slip ring and continue to run.

Alan

Do you for sure have voltage at the red wire - start there - this is required for the parking circuit - this goes to the track as described... monitor the red wire when you have the release motor running.

Alan