Brakes, dilemma.

Clamp on DC amp meter would be a better test.

ALL the Breakaway switch does when activated is put FULL 12 volts to the Trailer brakes. AS long as you have a GOOD Trailer battery. An easy test is to simply connect the Trailer to your Truck. PULL the Break away lanyard loose and then attempt to drive forward(NO truck brakes at all). Have someone WATCH all 4 wheels and tires ALL should be locked up and drag. It is best to do this on dirt or gravel lot. Concrete will not be a real problem for this test, but it is easier to drag on Dirt or Gravel. This will tell you that the Shoes and magnets are in working order. If you have a Wheel not locking up you then test the 2 wires going to that Brake and see if you have Ground and 12 volts. If NOT, then find where the open circuit is by the axles. If you DO have 12 volts then the Brake shoes are probably not adjusted correctly. Doug

This is an unusual problem. Most of the time when we hear about brake problems it is about too little breaking. Your test is to see that the brakes are operating. The fact that they have worn tells you that they are. Your compass test tells me that you are getting some voltage from somewhere that you shouldn't be. That being said it must be limited as full power to the brakes would leave them smoking hot driving down the road.

If the compass thing is accurate, sounds like power is going to the brakes all the time on 3 wheels. Time to get out a voltmeter and test them one by one. Then trace the wire back. It could be a wire rubber through and it picking up power somewhere, or the switch is letting power through, but if it was the breakaway switch all 4 wheels would have power and not 3. Whatever it is , it dosen't sound fun.

Learjet wrote:
Clamp on DC amp meter would be a better test.

I have seen LEO use the compass to check brakes in a roadside safety check. To tell you anything you need to hold compass near hub, but not so close that needed responds to the metal, apply brake, watch for needle to respond. The most it can tell you is there is power to magnet(s)
Yes, the AMP meter would be better, but bet a larger percentage of people have a compass.

dougrainer wrote:
ALL the Breakaway switch does when activated is put FULL 12 volts to the Trailer brakes. AS long as you have a GOOD Trailer battery. An easy test is to simply connect the Trailer to your Truck. PULL the Break away lanyard loose

BAD ADVISE! Unless you tell them to disconnect the light cord. There is a chance the brake controller will be damaged by power back-feeding if the pin is pulled while connected

and then attempt to drive forward(NO truck brakes at all). Have someone WATCH all 4 wheels and tires ALL should be locked up and drag. It is best to do this on dirt or gravel lot. Concrete will not be a real problem for this test, but it is easier to drag on Dirt or Gravel. This will tell you that the Shoes and magnets are in working order. If you have a Wheel not locking up you then test the 2 wires going to that Brake and see if you have Ground and 12 volts. If NOT, then find where the open circuit is by the axles. If you DO have 12 volts then the Brake shoes are probably not adjusted correctly. Doug

Learjet wrote:
Clamp on DC amp meter would be a better test.

+1

Looking for about 3 amps per wheel when activated by pulling the pin or manually applying the brake controller. Put the clamp around each feed wire to see what is working.

We usually run on 3-4 with prodigy p3. Boost set at 1-2. You may be running a little too high. Is your 5th wheel pushing the truck when braking?

Leo using a compass to determine braking action won’t stand up alone in court.

If a defective breakaway switch was applying voltage to the brakes with the pin in place, then you would have full voltage to the brakes (or at least 3 of them in your case) and several other things would have happened in 13k miles towing. You would have a very difficult time pulling the trailer, your fuel mileage would be less than 1 mpg, the plastic breakaway switch would have melted in about 1 hour, the wheel bearings would have overheated and failed from too much brake heat and tire wear would be terrible. Oh, while stored w/o shore power, your battery would be dead in about one day.

You didn't say when you did the compass test if the truck was connected or not? But maybe you didn't do the compass test correctly? You could jack up each wheel and see how hard it is to turn by hand. It is possible that the 3 wheels had the brakes adjusted too tight. Also, maybe you are riding the brake pedal and slightly applying the brakes while towing. And there are probably other potential causes. The 4th brake is ok most likely because it actually has an open circuit someplace and is NEVER working.

JRscooby wrote:

Learjet wrote:
Clamp on DC amp meter would be a better test.

I have seen LEO use the compass to check brakes in a roadside safety check. To tell you anything you need to hold compass near hub, but not so close that needed responds to the metal, apply brake, watch for needle to respond. The most it can tell you is there is power to magnet(s)
Yes, the AMP meter would be better, but bet a larger percentage of people have a compass.

dougrainer wrote:
ALL the Breakaway switch does when activated is put FULL 12 volts to the Trailer brakes. AS long as you have a GOOD Trailer battery. An easy test is to simply connect the Trailer to your Truck. PULL the Break away lanyard loose

BAD ADVISE! Unless you tell them to disconnect the light cord. There is a chance the brake controller will be damaged by power back-feeding if the pin is pulled while connected

and then attempt to drive forward(NO truck brakes at all). Have someone WATCH all 4 wheels and tires ALL should be locked up and drag. It is best to do this on dirt or gravel lot. Concrete will not be a real problem for this test, but it is easier to drag on Dirt or Gravel. This will tell you that the Shoes and magnets are in working order. If you have a Wheel not locking up you then test the 2 wires going to that Brake and see if you have Ground and 12 volts. If NOT, then find where the open circuit is by the axles. If you DO have 12 volts then the Brake shoes are probably not adjusted correctly. Doug

I have never in 42 years had a Back feed. BUT you are correct. To do the test with more safety, disconnect the 7 way plug and then pull the lanyard. Doug