Auxillary Battery Issue in '91 Fleetwood Montara

[alaskantraveler]

So I recently purchased a 1991 Fleetwood Montara. Its a base model that did not come with a generator. The coach batteries had been disconnected when I bought it. (not sure why). The batteries were bad, so I replaced them with new 12v batteries running parallel. Before now the coach lights only worked when the key was on which is obvious because the coach batteries were not hooked up. So I hooked up the coach batteries how I believe they should be hooked up in parallel. There were 3 ground wires. One very large one, one medium one, and one small one (I believe the sm. ground is for the LPG valve) all black wires. When we hooked it up the coach lights still did not work. So then we turned the key on. Immediately, the small ground wire from the chassis battery to the sidewall inside the engine compartment got hot and melted within seconds. So now I don't know what's wrong, first why didn't my coach lights work once I hooked up the coach batteries again? Second, there must be grounding issue why did the small ground wire on the chassis battery cook? Any ideas? I believe I hooked up everything right, but it was all taken apart when I got it so I will review that more.

[alaskantraveler]

OP here. The wiring is consistent with black neg/ red positive. There are not white wires. I will check with a volt meter to ensure. It is possible that as someone said before the a DIY replaced wires with the wrong color.

[MrWizard]

IF ? you have red and black at the battery

red is positive and black is NEG

IF ? you have black and white at the battery

black is positive and white is NEG

if you have ALL three colors, red black and white

you need to verify every single wire

in all cases where you don't know what has been done, you should verify ALL wires

[enblethen]

Trace the wires.
Positive should go to circuit breaker or fuse
negative should go to ground

[Jim]

A RV typically follows the convention of DC battery wiring having Red Positive and Black Negative. Then the AC wiring convention is White - Neutral, Black - Hot. There may be a couple white wires going to a ground in the battery compartment but that would be unusual. Usually the AC/DC system wiring is kept separate. You typically wouldn't find any Black AC wiring anywhere near the batteries unless a DIY'er was doing something in there with it.

For a RV as old as OPs, I'd suspect it follows the Blk-Red convention in the battery compartment. At least for the thick Pos/Neg cables. However, because he's not the first owner, anything could have happened as far as battery wiring goes. And what I think is that one of the positive wires (going to a battery positive post) might be black, and perhaps was wired to the chassis ground.

If the OP could take some pictures and post them here, we might be able to do a better job of helping.

[enblethen]

Black is positive!
White wires are ground.
Trace out the large white wire, it should go to ground.