Wiring harness issues sound familiar. We traced ours to faults in the fuse box itself.

Welcome to the MkIII ITB club. If you want to send info and a picture, we'll put a note on our site to share your car. Or if you have technical hints you've discovered, we can put them at http://www.it2.evaluand.com/gti/tech.php. We had this idea about being a clearinghouse of sorts for info on these cars, if you want to share.

Kirk