ok, I got things working and wanted to follow up.
A. Symptoms:
I have a coupe. The rear hatch release only worked from the driver's footwell switch. I had a bad microswitch in the hatch, which is activated with the door key. When I replaced the microswitch, immediately after engaging the switch the fuse would blow (shared with front footwell circuit).
B. Research:
After comparing schematics between 944, 951, and 968 I determined that:
1. There was NO short in the rear hatch wiring.
2. The hatch rear motors (944,951,968) all have 4 terminals. On a 968, the front footwell connects to two of them and the rear microswitch connects to the other two. There are at least 3 different wiring scheme between 944, 951, 968 in how they connect to these 4 terminals.
3. There are two kinds of automotive pigtails attached to these motors; a square connector and a round one. The 968 has a round connector, while the 944, 951 has either a square one or a round one (same as 968). I am not sure exactly which 944,951 have round connector shared with the 968.
4. I had a stock 968 harness for the rear hatch circuit.
5. I determined that my rear hatch motor came from a 944/951 with the round connector. It was not a 968 motor.
6. Both the footwell switch and the microswitch in the rear have three pins. One pin is ground, another is positive, and third sends the signal to the motor. By default, the open position from each switch sends ground. Upon activation of the switch they send a positive signal.
The signal wire for the footwell is Red w/ White Stripe. The signal for the rear microswitch is White w/ Blue Stripe.
C. Debug:
Upon further review the 968 motor has an additional diode installed on the outside of the motor housing. I decided to try modifying my 944 hatch motor by installing a couple different diodes to resemble how a 968 motor is wired. This fixed the fuse from blowing when I engaged the microswitch. The rear hatch light would dim when I hit the switch but the motor would not turn. Not knowing what else is different between the 944 and 968 motors internally I decided to go with a different approach.
D. Solution:
I decided to modify the 968 wiring harness to support 944 motors with the round plug. To do this, I would share the same motor input for both front footwell and the rear microswitch as all Porsche models supported at least one primary switch. However, since in a 968 we have two switch which actively send a negative signal when not engaged, we can not simply wire them together as this would cause a short. i.e. one switch pulling high when the other is pulling low.
Since I already bought a set of diodes, I created a little passive logic Y harness out two diodes. This logic harness has two inputs and only one output. I used spade connectors on all connections. Male spade on the output, and female on the two inputs. The output would connect the cathode "gray strip" side of the diodes together creating a shared input to the motor. The input side of each diode, the anode "black side", would attach to the front footwell and microswitch outputs signals; Red w/ white stripe and White w/ blue strip respectively. The diode prevent a positive signal from one switch upon engagement from feedback back into the other switch which is pulling the signal to ground. Avoiding a short.
I installed this device into the 968 harness at the connector (female side) just before it connects to the motor pigtail connector (male side).
I cut the Red w/white stripe wire on the 968 harness so I could attach my logic harness. The side of the Red w/white strip going to the motor I attached a female spade connector. I then attached the male spade OUTPUT from my logic harness. This would the shared cathode side of both diodes, to make sure current only flows toward the motor. Then the other side of the Red w/white strip wire which goes back to the front footwell, I attached male spade connector and ran it into one of the diodes inputs (anode side) on the logic harness. At this point you should be able to test the front footwell switch to make sure it still is working with the diode inserted midspan going to the motor. Assume all is ok, now proceed to cut the White w/ blue strip wire on the harness. The side going to the motor, we will not be using. So either wire nut it off, or attach a female space connector on it in case you want to revert back the cut you just made. One the side of the white w/blue strip wire that goes to the microswitch attach a male spade connector and run that connector into the other diode anode end (the remaining female connector) on the logic harness. Now you are ready to try the microswitch.
That's it. You now have a 968 harness which supports the 944 motors with the round plug, which should be in more plentiful supply than the 968 motors. If you ever find yourself a 968 motor and want to revert, simply remove the logic diode harness and reconnect original Red w/white strip together as they have male and corresponding female connectors already in place. Same with the White w/ blue stripe connection.
in terms of diodes, I used a pair of N5406.
p.s. you don't need to add a diode on the 944 motor, since my solution abandons the effort to use the other two terminals on the motor. Just focus on share the same motor terminals inputs as the front footwell switch.
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Now just have to figure out how to pull out the old microswitch from the hatch and install the new one in its place.
Anyone?? not obvious how to remove the old one.
