hi pete, i have a 94 300 tdi without the black box and mine went on the fritz. you need to speak to ian i think his name is at www.remotekey.com.
he was very helpful and sorted my problem out. hope this helps
ade
hi freeagent. not sure if this is much help but had a similar problem on my 300 tdi. it came down to the reverse switch wire from the gearbox had rubbed through and was popping the fuse when ever the ignition was switched on. mine was easy to get to. might not help but wortha look under the car before you start pulling your hair out