[ischmitz]

There are two ways to accomplish this:

1. Wire up the CEL of the ECU to a light. That way you can flash out any potential error codes. The procedure is explained in the Porsche WSM. Essentially you hold the throttle all the way down while turning the ignition to ON. Once the CEL begins to flash release the pedal.

2. Wire up a stock 964 or OBD plug and use the Hammer or a DurametriIc cable.

Being able to read codes is invaluable IMHO unless you wanna throw parts at an issue.