1999 Vangaurd Cutaway Class C electrical issues

[mr_p1]

I am posting for a friend of mine who just bought a used Vangaurd Class C. The Motorhome is in overall great condition, but there is one issue we found. When running off the house batteries we noticed the fridge, furnace, and tank level monitor will not turn on. Everything works fine when running off A/C power. There is a switch inside that has 3 positions (generator/house/converter). What we observed is that when switched to converter (motorhome plugged into AC) that all the DC fused lines are at 12V as they should be, but when we switch to the house batteries all the DC fused lines measure -12V. These measurments are taken inside the fuse/breaker panel. We also measured the same thing at the back of the fridge. The fridge will work off propane and 12VDC as long as the motorhome is powered through the conveter and the the motorhome is getting AC power.

Does anyone know why this is? Is there something wired backwards, or is a -12VDC ok? The lights, waterpump, and water heater still turn on when switched to house battery, just the fridge, furnace, and tank monitor that don't turn on.

Thank you,

[mr_p1]

Thanks for the replies everyone. So the batteries were hooked up backwards. They looked correct until I crawled under the motorhome to see that what I thought should have been the positive wire went to the chassis frame. All is good now.

[Mandalay_Parr]

Old-Biscuit wrote:
IF batteries are hooked up backwards.....the large fuses on converter should have blown. They are there for that reason (to protect from reverse polarity). If blown you wouldn't get 12V DC power from batteries.

If the converter doesn't work, you can still get 12volts from the batteries.

Jerry

[Old-Biscuit]

IF batteries are hooked up backwards.....the large fuses on converter should have blown. They are there for that reason (to protect from reverse polarity). If blown you wouldn't get 12V DC power from batteries.

[Mandalay_Parr]

mr_p wrote:
I would have thought you would be shorting the batteries if they are connected backwards, as it looked like the are connected to the chassis frame. The battery compartment is small so was hard to see, so I will double check it, perhaps pull the batteries right out.
Thank you.

The batteries will be reverse polarity...not shorted.
Keep us posted.

[Mandalay_Parr]

PaulJ2 wrote:
I would say batteries are connected backwards, easy to do. Less likely the switch wires would ever be messed with. Lights don't care about polarity, some appliences care and others not.

X2

[mr_p1]

I would have thought you would be shorting the batteries if they are connected backwards, as it looked like the are connected to the chassis frame. The battery compartment is small so was hard to see, so I will double check it, perhaps pull the batteries right out. Thank you.

[PaulJ2]

I would say batteries are connected backwards, easy to do. Less likely the switch wires would ever be messed with. Lights don't care about polarity, some appliences care and others not.

[mr_p1]

Yeah, I know my leads were not reveresed, I would hold them there and watch the voltage go from positive to negative just by switching from the converter to house batteries. The problem is, I do not know what wires are reversed, at the switch? I don't want to short something out and cause more damage. I can't even pull the switch out from the wall, there is zero slack in the wiring.

Thanks for the responce 🙂

[2oldman]

Boy that is a puzzle. It *almost* sounds like the batteries are in reverse polarity. But if that were the case, the things you describe as running would not.. or run backwards.