Quote Originally Posted by vnx205 View Post
I expected a poor contact in or near the bulb socket too, but all the connections and contacts were quickly eliminated as the cause of the problem.
If there had been a dedicate earth to the chassis near the light, things would have been much easier. What made it difficult was that the earth wire from the light follows the live wire into the large bundle of wires that supply all the rear lights. It is encased in that corrugated split sleeve and the whole lot is mostly inside the chassis.
Even though I am sure that, as others have suggested, a separate earth will solve the problem quite simply, I am still curious about the way the wiring is set up.
Is there an earth at the other end of the wiring loom at the front of the chassis near the firewall? If so does it earth just the reversing light? All other lights work perfectly, so it can't be a common earth. What possible reason could there be to run an earth wire all the way to the front of the vehicle to earth a light at the back of the vehicle?
By the way, thanks for all the helpful suggestions such as using test lamps and for all the explanations which have helped me get my head around a few of the issues involving electricity.
I have not had this sort of problem on my 110, but have on Series Landrovers. In their case, there is a common local earth on one side at the back, and there are multiple plug bullet connectors that join the different earths together - these are where the problems commonly occur. I know that on the 110 (and presumably the 130), the actual light fittings come with leads about 50cm long that plug into the main harness, both earth and live, and this is where I would expect your problem. It is possible the connectors are inside the corrugated plastic.

John