VW Cabrio Starting Issues

My 98 Cabrio has a haphazard start/not start syndrome. With increasing frequency there is no turnover when key is turned. I’ve had a major tuneup, the clutch safety switch replaced at my request, and the VW dealer saying it was an after manufacture floor mat that kept the clutch from being fully depressed. Sometimes, when not working a hard thump on the clutch against the floorboard will start it up. My service place and the dealership both say they can’t diagnose unless it isn’t starting. And when the car is with them it seems to start. It may start for a dozen times and then choose not to start, only to turnover the next morning. There seems to be no particular pattern.

It’s driving me crazy. Any recommendations from similarly plagued VW owners?

A friend of mine had the same problem with her '02 Cabrio. I wasn’t able to find the root cause because my wiring diagrams were worthless. But, I did notice that the reason for the no start was that the ECU was not getting power. Points to a bad relay or such.