Towbar electrics

[bigherb]

You can do it how you want if there is only the likelihood of towing your own caravan otherwise using 5 would create a dead short if you connected another correctly wired late plug. You also need to check your caravan wiring as how pin 4 is disconnected from the interior lights/caravan battery when towing either a change over relay switched by pin 2 or 6 or just a manual switch.

[CJH]

Thanks Bigherb. I want to avoid wiring that makes either the van or the caravan incompatible with standard wiring - you never know what either might be hooked up to in the future.

I'm pretty sure the caravan has one of the Plug-in Systems panels - not the PMS3, but I think it's wired the same.



So old-style wiring - separate charging (pin 2) and lights (pin 4) wires, with a manual switch to select either 'car' or 'van' battery as the caravan supply.

So I had another thought. For on-site use I could have a 12S extension lead (2-core, heavy) that joins the camper's pin 4 (permanent live - connected to the leisure batteries in my case) to the caravan's charging pin (pin 2) (plus earth's of course). This would allow the caravan to share the camper's leisure supply, by creating a bank of leisure batteries. So of course I need to pay attention to the relative charge levels when connecting up, but that's no different to the normal 'engine running' situation.

What this also means is that any charging source connected to either vehicle will service the whole bank. So hook-up mains charging in the caravan will reach the camper's leisure batteries too. But the main reason would be to allow the caravan battery to benefit from any charging current coming from my camper's solar panel.

I don't think there are any significant dangers in this. One (unlikely) scenario - if the caravan and camper are both plugged in to different parts of the campsite's hook-up circuit, is there a chance that their earth's could be at significantly different potentials? By linking the earths of the two vehicles I would create a link between those two parts of the hook-up circuit I think, if the mains chargers in both vehicles were on at the same time*. But this cable would be for use when there's no hook-up. If anyone is still reading (well done!) and following my ramblings, are there any other dangers I need to think about?

*E D I T: Probably not in fact, since the chargers use transformers - I think this means the battery negative is not tied to mains earth.

[CJH]

The bit of loom I bought from a breaker arrived today:


I cleaned it up a bit, trimmed the wires and made a breakout adapter.


This should sit between the plug and socket in the electrics black box in the engine bay, to give me easy blade connector access to the main 12N towbar socket connections.


All the wires have the same colour either side of the plug and socket, apart from the grey+white wire. That's the colour of the fog light wire at the light cluster. However, it turns into a pair of black+blue wires the other side of the plug and socket, and that's the colour of the reversing light wire at the cluster. So I won't know which circuit this is until I test it tomorrow.

[CJH]

Interesting - in my van that grey+white wire is the same colour either side if the plug and socket, but as said above it changes to black+blue in the bit of loom I bought. Maybe a later/earlier version with a different convention. Still, no matter - a straight-through adapter is a straight-through adapter, regardless of the wire colours. And in my van that wire is the fog lights.

So I have all the 12N circuits in that one adapter:

Left Hand Tail: Black+Grey
Right Hand Tail: Red+Grey
Left Hand Indicator: Black+White
Right Hand Indicator: Black+Green
Brakes: Black+Red
Fog: Grey+White

[CJH]

Whilst cramming my new breakout adapter and the new wiring into the black box, this thing started to annoy me.


So I opened it up to see what it is - turns out it's the world's biggest fuse holder. Is it a factory fit? Is there any reason it has to be so big, given that the fuse inside it looks the same size as a conventional ceramic fuse.


I haven't traced which circuit it protects yet, but is there something special about this fuse? It's an 8A fuse, but it looks suspiciously different from those in my fuse box. Is it a quick blow fuse or something? Does that justify the huge fuse holder?