RV Repair: RV 12V System, loretto mn, master electrician

Question
Dear Garry: I recently bought a 1993 Terry 29S Travel Trailer. When I bought it, the 12V system worked fine. Now, the 12V system does not work, at all, when the  trailer is not plugged in. Here is what I have done so far, a) Checked the circuit breakers, b) pulled and checked all fuses and c) opened a panel near the front of the trailer where wires enter the floor/subfloor looking for a fuse or breaker. My older 1989 Terry 15 foot, had a fuse next to the battery that would get shorted once in awhile. So, I have been looking for a fuse, or circuit breaker that could have tripped that is causing a "dead" 12 V system. I mostly RV while plugged in so this problem hasn't stopped my camping, but do like to run the water pump after dumping the waste tanks. Also, some day I will need the 12 V system.

In the month i have owned the camper, the airconditioner caused a circuit breaker to trip. I reset it and no problems since. And to make things tougher to solve, I bought the camper from a friend of mine who is a master electrician! He is stumped also, since he never had a problem in 12 years of owning the camper.

Any help in locating this fuse/circuit breaker would be helpful. The owner manual wiring diagrams show one on the system, the text says the battery should be protected with a fuse/breaker, but I haven't found it yet. Thanks for your time,

Sincerely,
Kent Torve
Loretto Mn

Answer
Kent,

   Usually there is a fuse or breaker right at the battery, if that is fine, depending on the type of power convertor you have, you may have a stuck relay.  On the Magnetek convertors of that year, in the lower section of the convertor assembly, there is a change over relay for the 12 volt system.  If it is stuck, this would cause the problems you are experiencing.

Garry