There is an extra 4-pin plug on the Motronics/engine harness on F1 cars (as well as the usual 3-pin ECU diagnostic plug for the Motronics ECU), but I'm not sure what it does. Here's a diagram I was working on a few days ago: Mystery Plug The F1 diagrams in the Workshop Manual show a 3 pin diagnostic plug, so I'm not sure if there are two diagnostic plugs.
