Dual purpose reverse/work lights
The most complicated electrical project I have embarked on to date is the rear lights. I had two different functions I wanted them to perform;
Work lights which must:
1. Run off the leisure battery
2. Be controlled from the back of the car.
3. Each of the two lights to be switched on independently.
Auxillary reverse lights which must:
1. Run off the starter/ alternator.
2. Both lights come on automatically when reverse is engaged.
3. Be impossible to activate from the cab while driving forwards.
4. Have a switch in the cab to disconnect them so we don't blind grannies in supermarket car parks.
5. Have no current drain at all on the starter battery when the car is not running.
I couldn't find any plans on the internet that would fulfill all these criteria. So I made my own plan, which is shown below. It is a little more complicated than is strictly necessary. But I wanted to make sure all my criteria were fulfilled. This achieved what I wanted, with pretty basic and easily obtainable materials, tools and skills. The other options for wiring lights are included in their own post here: Aux light options.
The general idea is that by splicing into the power feed for the factory reverse lights, that can be used to activate a relay that switches on the auxillary reverse lights. However these relays can only actually turn the lights on if the dashboard switch is closed (and the ignition on); completing the connection between the battery and aux lights.
Finding the correct wire to splice into...
This is the real crux of the operation. The procedure for this is the same for any vehicle, not limited to the D2. A good place to start is the Haynes manual, check the wiring diagram for the reverse lights and you should be able to identify what the colour of the power feed should be. In this case, it's supposed to be green and brown. Next, unclip the reverse light housing. This is easy, use the big metal clip on the inner end of the light cluster, if you reach up from the inside of the bumper. In a D2, there are three wires going into this cluster, one is red/yellow (rear fogs), one is black (earth) and one is green/brown (reverse lights).
I double checked at this point using a mulimeter. This is also the technique for working out which is the correct wire in the absence of a manual.
Step 1: Insert the multimeter probe into the contact for the green/brown wire, with the ignition off. It should read zero.
Step 2: Turn the igniton on, DO NOT START THE ENGINE, engage reverse with the handbrake on, parked on the flat, check for a 12V signal. (below)
Step 3: Put it in park, should read 0V, turn on the headlights and rear foglights, make sure the voltage is still 0V (In other vehicles, turn on anything else in the same light cluster).
Step 4: Repeat all steps for the other contacts. Ensuring you have identified every wire and what it does. Check the red/yellow is indeed the fogs (below).
Now you are confident you have found the correct wire, cut it. I tried to be clever and follow it back into the vehicle, but I ended up cutting the wrong one. I therefore advise making the cut close to the light cluster so you are absolutely sure you are cutting the correct wire.
Final check, see if the light works now you've cut the wire. If no, you've cut the right one. If it does light up, you've cut the wrong one. You can solder or make crimp connections to add your wire for the relay(s) (yellow/green in my case). I opted for the crimp option as soldering is annoying and I never seem to be able to do it right. (If in doubt, stick with what you know).
Relays
My design uses two normally open relays, as I wanted to be able to turn the lights on individually as worklights. You could just use one if this was not necessary or you only have one light. I will make another post with the different options for aux lights. The photo of the relays is wildly confusing but here goes... The yellow and green comes from the live feed to the factory reverse lights, (seen above) the blue goes to earth. These two activate the relays when the factory reverse lights are on. The red cables carry the current that actually powers the lights. The red wire in the foreground is the live feed from the battery, the ones on the other side lead to the lights themselves. After wiring everything up I zip tied the relays up behind the plastic trim in the back of the car.
Piggyback circuit
I wanted the switch in the cab to light up when the aux lights are connected, as a visual indicator before engaging reverse. However I didn't want that light to be on when the car isn't running, so there is no drain on the starter. The piggyback circuit which holds the switch and relay for the aux reverse lights serves this purpose. Find a fuse which is only powered when the ignition is on. In the D2, I found fuse 31 (heater I think?) is only powered when the ignition is on. You can check this using a multimeter or indicator light. Therefore by piggybacking my switch circuit off it, I ensured there is no current going through the switch light and relay when the ignition is off, and therefore no drain. The piggyback is shown below, along with the relay it supplies and switch to activate it. I bought about five piggyback terminals off the internet for £6 or something. (Cheaper than a single one from Halfords...) Just make sure you get the right size for your vehicle.
The switch simply protudes from a panel gap at the moment. I will endeavour to get it linked up to a factory switch, but I need a bit more time and research for that. More to come on that in the future. There's loads of metal under the steering wheel to earth it to. Take your pick. On the relay, the brown wire is coming from the switch, the blue is the earth. The red wires carry the current for the lights themselves.
Work lights
This is by far the more simple of the two circuits. If you are new to this sort of thing then I advise just doing the work light circuit and leaving the reverse function for the moment. It's just a power feed from the leisure battery which splits, with an in line switch on each line. These then join the wires to the lights themselves at the downstream side of the relays. This keeps the two lights separate when used as work lights. Red wires are power feeds to the lights themselves, the blue wires are earths for the LEDs in the switches. (yes I know the switches don't match, life's too short to be perfect...)
Wire routing
It's mostly a matter of just wiring as shown in the diagram, check the earth points are good before testing the lights. I used the mounting bolts for the rear headrests as an earth, they worked well. The LEDs in the switches, as well as the relays, are earthed to a factory earth point near the third row seatbelt mountings. These are shown below. If you remove the head rests there is a convenient hole through which I sent the wires out. No need to do any drilling. They then run round under the rain gutters and up the rear rack to the lights themselves. The live feeds from the batteries pass behind our storage box on the drivers side to the leisure battery. The reverse light feed carries on via the center console, through the rubber grommet in the firewall to the engine bay and the starter battery.
Materials
I used 10m of single core 30A wire for all lines carrying current that would actually power the lights. Those wires on the outside are 30A dual core. The wires carrying current in the relay circuits are a mix of smaller calibre wire. The system includes three SPST rocker switches and three normally open relays. It would be possible to replace the two rear relays with a single one with dual contacts. But I didn't have access to one of those. To finish it off, I used rather a lot of crimp terminals. You can never have too many crimp terminals in your tool kit.
The lights
The lights themselves are 'WOW LED', I got them for £14 each at one of the Land Rover shows. They're 18W, 1440 lumen, 60 degree LED floods. They're plenty bright enough for this purpose. I would go as far as saying that using both together is too bright for comfortable work light use. You can barely even look at the car with them both on. The brackets have rusted quite quickly, but on the whole I am very happy with them.
Other options
I will make another post with different wiring options for reverse/ work lights. Everyone has different requirements and I think it's useful to see the strong and weak points of each circuit.