I thought that I had much of the wire harness work done already, but when I started looking at the details from my previous work using an '03 Audi V8 I realized that almost none of it matched the '98 harness. The 2003 uses Bosch Motronic ver. 7.1 and the 1998 uses ver. 5.4.
Here's a problem: The transmission control module connector wired into the ABZ engine harness is different than the Porsche 986 Tiptronic connector. It looks the same and plugs in, but the wiring is different. The ABZ (1998) ECU and TCM do not use CAN at all. I had expected some problems with software/firmware, but this could lead me straight to transmission Limp Mode or physical damage to the TCM or transmission.
My plan is to re-wire the TCM connector on the Audi harness to be as close to the one in a 1999 Boxster as I can make it. There are some specific connections on the 1999 Boxster diagram that aren't included in the 2001, so I'm guessing that the '99 CAN bus carries less of the load.
If I was running with a manual transmission, there would still be some quirks from the missing signals from the automatic transmission unless I
chipped the ECU. Pricey, but effective. At best, running with the Tiptronic transmission, there will be some problems. My goal is to get it mostly functional and driveable even if it means using a few work-arounds to keep it out of Limp Mode.
I have two fall-back plans to keep the Boxster for the Challenge if this swap turns into a complete mess. One is to stay with the 2.5L engine and work on making the car as light as possible. The car is running decent right now and could do the Challenge -not competitively, but still fun. The other is to pull my 2003 Audi 4.2L engine out of another project, fit it into the $2,000 budget, and hope the CAN signals from that will work with the Boxster TCM and transmission – the wiring looks the same.