I had this problem on my 95 LWB. The RAVE service manual electrical trouble shooting material is pretty good it just takes some time to understand. My glove box light switch was intermittently shorting out the circuit, (the switch had cracked and internal parts touched the metal holder) which includes the tail lights and several other components. I started at the fuse box, and slowly disconnected parts of the circuit checking for a short to ground each step. Start with the circuit diagram and work through each leg, connector to connector - checking for a short to ground or no 12v delivered - you will eventually find the problem. Think of it as bonding time with your Rover.