If your transfer box is fitted with a diff lock, you will have a selector shaft poking out of the top of the front output housing. Describing where this is and how to feel for it is hard!
The selector shaft pokes through a round metal cover that is bolted to the TOP of the transfer box with 3 bolts. If you lay on your back under the vehicle with your head under the front propshaft and your feet pointing backwards towards the rear axle, you could feel for it by using your left arm to reach up to the left hand side of the front propshaft and then on top of the transfer box.
A mirror would be easier!
Anyway, it is worth noting that when you engage diff lock in a Disco with ABS/ETC (as all Disco II's have) several important things happen:
1. Hill Descent is turned off
2. Electronic brake distribution is turned off
3. Electronic traction control is turned off
There are a couple of switch configuration options depending upon whether the Disco is pre or post 2003 - but in either case, the switch is wired up to the SLABS ECU which illuminates various lights on the intrument pack. On pre 2003 models for example, Land Rover didn't really get it sorted properly and engaging diff lock made the diff lock warning light, PLUS ETC PLUS EBD warning lights come on on the dash.
As the ETC and EBD warnings were effectively stored as volatile error codes in the SLABS ECU, they could only be extinguished once the SLABS ECU did a reset and system test. This happens every time you switch off/on the ignition and so Land Rover recommended that owners only disengage diff lock with the ignition switched off
Needless to say, they sorted it for later facelift models..
Just noticed that I can attach stuff to these posts, so I will attach a picture from the workshop manual of the diff lock selector shaft (this is for pre-03 model).
