Some Simple and Important Brake Test

in my brake upgrade attempts ive come up with some simple quick electrical testing for the brake systems on our trailers. these for tests will tell you lots about the electric brake system

So here are four simple brake tests, all done at the 7 pin connector, all pics have the top of the 7 pin toward the top of the picture. I'm using an inexpensive voltohmmeter(VOM), it has a current measuring capacity of 20 amps

first picture is a simple battery voltage test at the 7 pin. black lead from the meter in the bottom right slot(ground), red lead in the top left(12v from tv). my reading is 13.55, normal considering I had just unplugged the trailer from the house





next picture is a resistance measurement of the braking circuit. black in the ground slot, red is in the brake slot. I'm reading 1 ohm, normal for 4-7 inch brakes



next is testing the battery under full braking load. voltage measurement method is the same as the first pic but ive activated the brakes fully with the white jumper wire. battery voltage has dropped which is normal



finally the current draw test. note that the red lead on the meter is moved and note the testlead positions on the plug. i'm activating the brakes through the meter. I'm reading 9 amps which is low, should be 12



obviously since I measured 12 amps without the whip to the truck in the circuit yesterday and 9 with it today, there is a problem in the 7 pin cable somewhere, not unexpected at all

edit: I repeated the last test but used the positive battery terminal for the supply and not the 12v in the whip. black lead in the brake slot of the 7 pin, red lead on the battery terminal. amperage was 12 amps. so the whip is good. the 12v supply wire in the whip is probably only 16 ga, brake wire is probably 12 ga, big difference