I have a 94 3000 V6 Pajero, and have noticed that when I switch on the lights, the bottom guages (i.e. voltage, oil temp and vacuum) go dead.
The battery has been tested and found to be in good order.
Anyone have an idea what it could be?

its a short in your gauge cluster most likely a ground wire got heated enough to melt your plastic off of the wire and when you turn on your lights the circuit then extends to that short and kills your other lights. you need to turn on your lights and test your cluster grounding wires for voltage. once you get to a part where you no longer have voltage you can find where your problem is.

Thanks, I'll give it a go.

yep have fun...(as i point to my head and pull a fake trigger) i hate electrical even though i know a ton about it.