DarylJ

So I tracked it down.

Here's the FSM wiring chart for the alarm module:



You can see the have you bridge ping 1+4 and 8+7, same as what Clark's says but their graphic must be an earlier version of the FSM, as it doesn't include the "BRIDGE ONLY FOR VERSION WITH ALARM SYSTEM".

So, tracking down what the 4+1 bridge does, I found that pin 4 ends up at terminal 86 on the DME relay, and pin 1 ends up at terminal 15 on the ignition coil. So you're going nowhere without this one.

Ping 8 traces down to A40 on the sheet to another sheet in location H43. Here's what we've got there:



Pin 7 traces into the central electrics on another sheet, and then goes to yet another. I don't think it's necessary to trace this one any further, because it obviously is what feeds the field current once the car is done with the starting sequence.

To sum it up - you can bypass an alarm with 1+4 and have you car run, but you will have to rev it up to 3k RPM to start the alternator if you don't have 8+7 bridged as well. Revving you car up to 3K RPM, while "normal" to many of you, is simply BROKEN. Fix it or don't fix it. It's up to you. But make no mistake, it's broken.

Josh B

Thanks Daryl for the in depth write up. I don't have the factory alarm on my car but I guess this still applies? I wonder if I need to find a new gauge cluster and see if that fixes the issue?

DarylJ

A few ideas ideas:
- From my research, the jumper on pin 8 should still exist (you should have the alarm connection - alarm or not), and pin 8 should be directly connected with D+ on the alternator. Someone on a thread on Pelican suggested that there is a plug that this wire goes through between the inside harness and the alternator and it's located near the brake booster. I'd check that run from the alarm connection to D+ on the alternator to see if you have continuity.

- Check pin 7 for voltage. When the car is started and running, it should have 12v on it. If not, you need to trace backwards into the central electrics from there. As I mentioned, I didn't trace any further, and I'm going blind looking at PDF on my screen. I'll be happy to trace that part down if necessary when I have my FSM in my lap back in the garage.

You can always jumper from the + on your battery to D+ on the alternator as well. Obviously, this is not something you can leave because you'll drain your battery, but it will prove that the alternator and voltage regulator are working properly (as in, you apply 12v to D+, start the car, and you should see the 14.whatever you normally see at idle after revving, but without having to rev the car this time).

mortymower

I am pretty sure that porsche chnaged the wiring diagram for the 87 on 951 by placing a resistor inline, so even if the bulb in the dash blows the exciter wire still recieves power. Granted, the line could be cut/shorted anywhere along the way, so I would try what daryl said above and jumper the line temporarily and see if it acts like it should.

On a much more simple note, have you replaced the belt, I had a front main seal leak that somehow got oil onto the accesory belt and it slipped until revved up. It wouldnt hurt to spray some brake cleaner on the belt and then some dressing and try it out... just a thought