RV Repair: RV 12V system, golden falcon travel trailer, falcon travel

Question
Hello Darren,
I just purchased a 1984 33' Glendale Golden Falcon travel trailer.  It's been sitting in a park for the past 20 years.  I've now got it on a vacant lot (without electricity) where I'll power it up from a generator.  
The problem is that the 12V lights inside the trailer work when I've got the 120V AC system connected to the generator, but won't work from the 12V battery (which is new and charged).  From this I'm assuming that the rectifier is OK, but there's a problem with the wiring somewhere between the battery and the power supply unit.  Most of this wiring can't be seen.  
I've considered tapping in to the 12V wires where they leave the power supply.  Using a 3 way switch, I could select to power the lights from either the battery or rectifier.  
Any suggestions would be appreciated.

Answer
Ron,

   I would check to make sure that the battery has a good ground connection first.  The easiest way to do this would be to unplug the trailer from shore power and take a test light or volt meter and with battery charged hook the negative clip or lead to a ground on the chassis and the probe or positive lead to the positive side of the battery.  If it has bad ground it wont light up or register voltage.  If it does then the problem is in the positive wire to the converter or there may be a problem in the converter itself.  If the ground doesn't fix the problem write me back with the brand name and model # of the converter and I can give you some additional things to check.  Good luck and Happy Camping.

Darren