Thursday, June 3, 2010
Posted by RV Doctor
I have an F-350 pickup pulling a Newmar Mountainaire fifth-wheel. I have been using a Jordan brake controller. The RV has three axles with six brakes. Until recently the RV braking has worked flawlessly. Last week while applying the brakes the amperage readings on the Jordan display, jumped up to 30-plus amps. Normally the readings are between 9.5 to 12-amps. On one of the next brake applications the controller emitted a puff of smoke and quit functioning. Upon inspection I find that along with the blown brake controller, the Ford under-hood fuse box, which controls the trailer charging circuit was also blown. Can you shed any light on this problem? I cannot find any apparent short circuit in either the truck or RV system. Could a shorted out brake magnet in one of the wheels cause these troubles? Could there be two different problems? --Rocky, (Livingston, TX)
Rocky, though it's possible you have two issues, I feel it’s unlikely. Normally, the larger brake magnets will draw almost 3-amps each under full load. Considering the safety ramifications, it would be prudent to remove each wheel assembly and inspect each magnet. It could be that two or more may be internally shorted. Each magnet can be bench tested if a doubt exists.
The fact that the Jordan measured no more than 12-amps leads me to believe that two of the magnets were not even in the system to begin with. Inspect as much of the brake circuit wiring on the trailer than you can eyeball and look for loose, worn or shorted connections. Check each connection behind the backing plates carefully. Where the brake wires enter each axle can also be an abrasion point. Also inspect the umbilical between the truck and trailer. If the cord was pinched at or near the hitch assembly during a hard right-hand turn for instance, both the charge line and the controller could become shorted. Check also that the controller is not wired through that charge line fuse. My educated guess is the problem lies within the brake circuit and/or charge line itself.