It was just a chat I had with the guy who services my car. He was completely baffled by it all but we were convinced it had to be more than a simple wiring issue as the mileometer, speedo and abs were affected at the same time. He had already checked the ABS sensors and they were fine. I could only think of the relay that would use all of those signals (i'm no expert on car electrics so that may have just been a lucky guess). I got the part from a specialist breakers (Douglas Valley Breakers 01257 472866).
And yes 19 year old cars always have something to keep you occupied. Mines the a/c at present