Just finished my first attempt at an annotated circuit diagram for The Duke. It’s a copy of “Figure 150” from the military manual, but I’ve put as many notes on there as I can so I don’t have to keep cross referencing.

It took bloody ages, but it should be pretty handy as long as the original is kept nearby to double check things that seem weird. There are also a few things on there that aren’t fitted to The Duke (fog lights for example) so I can use that diagram as a base to add, delete and move things until I get something that actually represents my setup.

Anyway, today’s puzzle is the Auxiliary Relay. Looking at the lights in the diagram, the side lights, tail lights, instrument illumination and number plate light seem to be wired (as you’d expect) to the 6-way light switch. The main and dipped headlights are wired to the headlight switch. Also very sensible. In amongst all these components, though, are connections to the crazy military stuff. The infra-red relay and switch and the auxiliary relay.

As far as I understand it, military vehicles come with a 6-way light switch with three positions for normal lights, an off position and two convoy positions. When the convoy light is on, all other lights on the vehicle will be turned off.

This is all very well, but I don’t have a six-way switch and I doubt I’ll be getting one any time soon. Therefore I need to work out how to wire the lights up to the civilian two-way switch, which has a setting for side lights and another for headlights.

Some useful information can be found in this article on converting from 24v to 12v. Obviously I wouldn’t consider such a thing, but it’s good to know what changes can be made if need be. I also noticed a mention of an ignition filter box which sits on top of the rocker cover and apparently “sells well on eBay”. Guess that explains the missing nut I noticed yesterday!

Some more titbits on the Land Rover forum: One bloke mentions the aux relay being used for “switching things that require both Ignition-on & the “Convoy Inhibit” off”. Sounds pretty sensible, but hard to get to grips with when the diagrams don’t show which connections are which on the relays.

Anyway, that’s what I’ve been doing today.