Thanks to all of you who have offered advise.
For those interested in what was wrong....
I first rewired the overdrive as the existing wiring was really dodgy....pretty simple job. That done I proved that 12v was being supplied to the solenoid and found no movement therefore I changed the solenoid....the replacement didn't work either when fitted although when I returned the unit to Canley's they tested it and said it was fine. I traced the problem to the relay which seemed to be working fine ie. gave a 12v output at the solenoid...However when the solenoid was under load (connected) the relay failed and the power supply was lost giving the impression that the soleniod was shot......tricky swine!!!
If anyone has any overdrive faults which they think are electrical I would start by changing the relay...only &163;10 or so.....then try the wiring..then suspect the solenoid. The best way to prove you have a working solenoid is to run a wire direct from the positive side of the battery to the solenoid power lead with the solenoid in situ and inspection plate removed. I tried to test the thing on the workbench with no joy...but in situ works fine.
Anyhow its all sorted now...next job...how to improve the handling!!!!!
Hope my blunders help someone else out.
Cheers Again
Jonathan