we were having braking issues on our 4000lb(loaded) tandem axle tt. ohm reading was around 3 ohms, good voltage at the 7 pin.
but the most important check of electrical performance is the current draw at maximum braking. it should be around 12-16 amps. resistances and voltages are meaningless numbers, you need to measure the current
a decent vom that reads up to 20 amps will do the trick
shown in the pic, I'm applying the trailer brakes from the trailer battery directly "through" the vom and the meter is reading 9 amps. this was part way into the rehab of the brake wiring, I went from 4 amps to 12.5 amps.
I replaced every wire, from the truck battery to the controller, to the truck 7 pin, new trailer 7 pin whip, new wire down both sides of the trailer.
I ran a new 10-3 cable down the length of the truck, used it for 12volt supply to the tt battery, brake and ground. I also ran 10-2 to the brake controller(power and brake) at the tt I used a new whip, new battery wires and new 12-2 to the brakes, one cable down each side. I did not cut the cable at the front brake, I stripped the wire enough to wrap the magnet wires around the cable then soldered and insulated everything. I used "liquid" electrical tape for decent weather proofing
