how to check the wiring to the Diff lock ???

Hi guys, while I'm changing my clutch fork I intend to check the wiring for the diff lock as it's been lit on my dash for for over a year and a half. This has happened since I changed the clutch last time and I reckon I trapped a cable somewhere, I've had the gears checked and it definately isn't in diff lock. The same applies to my speedo...caput. Got a multimeter and ready to go....only I can't figure out which wire it is (looking through the hole where the centre consol used to be), any idea which colour it is . Also the speedo, there must be a connection near the bell housing somewhere which has been buggered. Can't find much info in the Haynes manual, any of you had similar probs and if so any tips.

Cheers all
Al