Wiring tip

Like most people I followed sloan's book for this swap and page 97 indicates the late 944 14 pin connector offering pin 3 as a source of +12 volts switched to connect to the PCM pink wire.

The problem with pin 3 is that the switched 12 volts comes from the DME relay. This relay can fail and your PCM will shut down.

In my 88 NA the two wires that originally went to the ignition coil (green, black), can power your PCM.
Connect the two wires together and now you will now have switched 12 volts on pin 1 of the 14 pin connector. This eliminates the risky feed from the DME relay.

This should work based on the wiring diagrams. Or if you're pulling out unused wires on the body harness, you could just delete the green wire and run the black wire back through the firewall and to your fuse block. The black wire at the coil connects straight to the ignition switch.

Just get your ignition positive at the ignition switch, that way you won't have to worry about any of the Porsche wiring problems.....

For a constant B+ source could the red/green stripe wire that goes to the DME be used since the DME is not being used? Or does it power more than the DME? I am finished with my wiring and thought of this after the fact. It could be removed, if it is not needed, to decrease the wires coming off of the battery.

That's what I've done, Arthropraxis. I've removed the DME relay and powered my PCM and gauges with it's turn-on signal from the ignition switch. And I've pushed the fuel pump output from my harness, which has it's own fuel pump relay, into the DME relay's output to the fuel pump.

Works, but not so pretty...



You can also see I've powered pin 9 of the G6 block deal. This jumpers the fog lights so they opperate independent of the headlights. This because I'm using the fog switch and wiring to the right front as a turn on/off for my accusump.

Rich

There's a hundred different ways to wire this stuff. If you are going for maximum reliability then Admin's method is probably best. I tried to find a good spot to fit my aux fuse block+relays and couldn't really find an elegant solution until I looked at the original fuse block and saw the spare relay spots. My original wiring is in great shape so I don't have any worries about continuing to use it.

For the switched power, I found that the G2 relay is basically a spare relay when key is in the run position, so I decided to use that to power my key power fuse block. The +12v output is pin 21 on block A, which is the empty block on the fuse box - you can use a 1/4" disconnect to that terminal or find another connector from a parts car for a more reliable connection. One of the other terminals on the same connector also provides constant +12v, so I'll be using that for my battery +12v fuse block. The fuse blocks are mounted inside my cruise control box which I cut the front out of.. out of the way and easy to get to.

For the fuel pump relay, I used the turbo cooling pump relay socket which sits in the spare relay section and is easily accessible. I only had to run the wire to the PCM fuel pump feed and a 15a fused line from +12v, the ground and fuel pump wire (grn/blk) come from the terminals pulled out of the turbo cooling pump relay socket. It uses a standard 30a tyco relay.