I'm getting a low level reversing light (i.e. not fully bright) when the side lights are switched on. It gets brighter when engaging reverse, so the switch is working (I checked the resistance on the switch and it is good). I have also still got the side light connection to the tow bar loom disconnected, so it can't be feeding back from the dodgy cabling I've got in there. Any ideas?
bad earth Next to the lights in the engine bay will be a brown wire fixed to the bodywork remove it and clean it all up
A possiblity for all your light problems - too much paint on the tow bar? I once painted a pair of T4 inlet manifolds to spruce them up, carefully refitted them and in doing so destroyed the earth path for the cut off valves and chokes.
The rear cluster earths disappear back into the loom, so I don't know where they terminate, but I can run wires direct to the main post near the battery. I measured 0.6 Ohms from the O/S earth to the main post and 1.0 Ohms from the N/S cluster earth. Is this enough to be a 'bad' earth? How does the bad earth actually work. If the return path has a high resistance, there is a residual Voltage on the earth at the cluster and this then causes the other bulb to illuminate? Where is the return path for the other bulb that allows it to light?
All the bulbs in a cluster are joined by their earths. If there isn't a path from the cluster to the vehicle body it finds a route through the bulbs and back to... Don't ask me! @matty
The bad earth thing normally arises due to current (that normally would go to ground) finding its way through the filament of another bulb in the cluster, as the earth connection is common to both. Try grounding the body of the bulb holders directly to the van body. It may be that your "earth" is connected some way away in the bowels of the loom, which isn't ideal. <edit> Zed beat me to it
But when it goes from the common earth through the filament, where does it go? Anyway, will run separate fat earth cables from each cluster to the main post next to the battery.
Without the direct earth on the rear lights the current can find its way back all sort of ways in your case the reversing light could go through the tail light bulb to the switch to the front side light and to earth it will always take the path of least resistance Earth faults can be a nightmare to find and can do some strange things i had on once if you put lights on the wipers came on it was a fault with the heater
A vote for original wiring here, I've never had a problem with it other than old broken spade connectors and the horn circuit getting broken..
Unfortunately, mine had been messed about with in a big way and was a complete mess, so it needed replacing. In hindsight, it would have been better to make up a loom rather than get the modular one as it would have been a better job. The modular one took a lot of fitting (as I discussed with Paul last week, the rear demist wire leads to the engine compartment!) so for the money was not great value.
Rear demist via relay in engine compartment for a more direct route for power to the demister from battery, relay switched by switch on dash... Demisters take a lot of power, so unless your wire is a big fat one, it'll be for a relay trigger. Your dash switch will either earth the trigger circuit or take 12V from a fuse and earth at the relay fixing screw might be better.
You've then still got to run a feed from the engine bay, up into the back of the van... which technically gives you a fumes route from the engine bay...
There shouldn't be fumes in the engine bay as your heating air comes from there, so technically that's not a problem.
Did as follows: Checked main earth post and found it was replaced when the engine bay was painted without scraping off the paint. Cleaned it up, tightened up and tested. Earth better, but same problem. Took out Firetec that was obscuring the N/S rear cluster and could see that the leisure battery was pushed up against the back of the cluster. Moved the battery and removed the cluster to find the rear light connection had been broken, bodged on and then fallen off so it was contacting something else. Reconnected and rear lights working. Moved on to testing the reversing lights. Got some weird stuff happening so cut off the twin connection at the switch to test each wire separately. Connect the O/S reversing light and it works. It has no effect on tail lights when they are switched on (i.e. both on when on, both off when off). Connect the N/S reversing and it does not work, but the N/S tail light comes on. Switch on the tail lights and the tail light goes out. The reversing light stays off too. No effect on the O/S tail light. If both connected, the effects are identical, although at one point earlier I did have the O/S brake light on when the reversing light was switched on. I have already disconnected the brake, tail and reversing lights from the towbar circuit to isolate that.
Looks like cleaning up the main earth solved some of the problems (eliminated the reversing lights illuminating when the tail lights came on), but not all of them. The N/S earth is still a problem, even though it runs to a point on the body. Just did a quick jump lead to the main earth post and the lights worked OK. Will hard wire this when it stops raining and test everything.
