Brake Madness

[vangoes]

Let me start by saying "electric brakes can drive you mad"! With that out of the way, my primary problem is low voltage at the brakes when hooked to truck. Now here is my confusion. Voltage at truck plug without trailer hooked is 12.4v. Hooked to trailer, the voltage at the junction box in the kingpin is only 7v but if I disconnect the blue wire feed to the trailer brakes the voltage returns to 12.4v. With this low voltage trying to diagnose the individual brake magnets is virtually impossible so I decided to unhook truck and try the breakaway switch route. Now, the voltage at the junction box is higher than the previous 7v but is still only 10.4 volts. If I again unhook the feed to the brakes, the voltage in the junction box jumps to 12.6v, and is the same voltage at the battery. To sum it up, there is voltage drop when ever the brakes are inline.

I decided to test each brake using the 10.4 volts that the breakaway was providing. Here are the results: Voltage 9.2 - 9.6v; Amps 2.3 - 2.5; resistance 3.4 - 3.5 with magnets disconnected and 1.1 - 1.2 with magnets connected. I believe the results are normal and expected considering the low 10.4v to start with. There is no one brake giving results outside the ranges of the others which tells me the magnets are all good.

I also believe the truck controller is good as is provides 12.4v when the trailer is unhooked.

If anyone out there has any suggestions to help me find the problem I would greatly appreciate it.