electrical burn out

[nevill3]

On my homebrew setup I inherited with my camper there is a wire that goes from the starter/car battery to the Zig unit. There is a corresponding wire going from my leisure battery to my Zig Unit. These wires are connected to the three way rocker switch that allows me to switch between using the leisure battery, starter battery or Off for the 12 volt electrics in the van.

I would check to see if the melted wires go to either your Zig unit, an eberspacher type heating system or to your fridge if you have one.

The fridge could also be your problem as that is one of the few things in a camper that uses both 12v and 240v. If the switch on the fridge is faulty could that not inadvertently connect your starter battery to the 240v system?? (It should have to pass through a relay triggered only when the engine is running so that the fridge can only be used on 12v whilst the battery is being charged.)
Was the engine running when the wire melted whilst on hook up?

The old wiring in these vans has often been added to over the years. Last year a wire that had been used to connect my Car Radio came loose and earthed itself behind the dash. Unfortunately the wire had broken on the battery side of the wire before the fuse and this created a short. The wires that melted on my van were an extra earth wire that had been installed by a previous owner for an extra cigarette lighter. The normal battery earth was OK but the thinner wire used to earth the cigarette lighter melted.
I learned that even though correct specification wires were used to install the leisure battery a subsequent lower specification wire melted on a system that wasn't directly connected apart from incorrectly sharing a common battery earth. This earth wire should have gone to the car chassis and not have been returned to the leisure battery (the cigarette lighter body was acting as an earth too so the current passed along this thinner wire and earthed through the cigarette lighter body). So a melting wire on one thing could be caused by something apparently unconnected.

Nev

[Oldiebut goodie]

I don't know why you are all so against using a return to the battery instead of the chassis, there is not always a suitable piece of bare metal to use. Most of my Merc's additional wiring is earthed direct to the battery as it was a fully insulated and lined bus originally with next to no access to metal and it is just as easy to feed two wires through same as one. (boats are always wired directly back to the battery/busbar as there is no chassis). The expense is not going to be much greater either in these small vans.
As above - people forget to use the same gauge wire for the return as the power though leading to the melting of the return.

[feardana]

Hi Nevill, no the engine wasn't running when the wires melted - we had just arrived on a new site, hooked up to the mains, were getting ourselves organised and maybe 30 minutes after we arrived i got the smell of burning plastic but i can't say for sure how long it had been before the wires started to overheat. I can say though that the fridge hadn't worked on the previous site we'd been on though the sockets worked to run phone chargers/boom box etc - the DC power seemed fine also, lights, pump etc were all working - our fridge, an old electrolux is supposed to work off the mains, gas and the leisure/car battery but i don't think it ever works on anything bar the mains - i didn't realize that the mains could be connected to the starter battery in the way that you describe - There is a selector switch on the fridge, (mains/12v/gas) - i'm not sure what you mean by "It should have to pass through a relay triggered only when the engine is running so that the fridge can only be used on 12v whilst the battery is being charged"

I'm going to assume for now that the second wire connected to the -ve terminal on the car battery is for earthing purposes and get an electrician to check that aspect out as well as to see if the wire coming off the positive is going straight to the split charge relay or not and also try to find out if there are any diy jobs done on the electrics outside of that.

midlife crisis said that "There's usually only one wire (other than the two red/whites)" coming off the alternator though on mine there are 2 wires, one brown one blue coming off the alternator and after running thru fuses these wires go from blue and brown to green and a darker green colour - anyone have any idea why there's 2 instead of one and where these might be going?

many thanks