Jaguar Repair: speed odemeter on 85 xj6 jag, service interval, interface unit

Question
hi mr howard my speed odemeter stop working on 85 xj6 jag. i replace meter in dash - and speed transiducer in trans- it started to work few days stop again what do u// think it could be.

Answer
HI James,

The speedometer and the pulse generator are not all there are in the system. The pulse generator is also connected to the Service Interval Counter, The Cruise Control, The Trip computer and an Interface Unit.

To test if any of these are causing a problem you need to disconnect the yellow wire from the Service Interval counter, the Cruise Control and the Trip computer. Then confirm with a volt meter that the Pulse Generator is producing a signal and that the signal is reaching the Speedometer and that the speedometer is powered by the green wire and the Black wire is a true ground.

Somewhere in all of that you should find the problem.

Howard