Another update...
Took the underbelly loose so I could check the wire and found it is 12ga, not 16 like I thought. They only had 18ga for drop and cross-wires.
Checked it with the truck idling and full gain, 9.1 volts at the rear main junction by the trailer axles. Better than with the breakaway but still not very good.
Next step was to optimize the trailer without re-running 10ga wire through the trailer. First, I replaced all the 18ga drops and axle cross-wires with some good quality, 19 strand 16ga speaker wire I had with really thick, flexible insulation. Soldered all connections, including the ground and power in the pin box junction box. Finally, the best change I made was to add a ground wire directly to the frame near the axles. This alone basically eliminates the resistance of a 30' piece of the 12 ga wire, and it shows.
Final measurement was 10.0 volts at the rear axle, so almost a full volt. Since the 16 ga drop and cross-wires would actually increase current and decrease the voltage, the current probably increased more than 10%. Unfortunately, I only measured current after the changes and was 3.6A in the worst case magnet(rear axle, opposite the 12ga main line). Total resistance of the system also changed from 1.2 to 1.0 ohm. This is with a $15 multimeter so the accuracy is questionable.
Also measured reistance of a few magnets and they showed 2.9-3.0 ohm. Measuring across 2 in parallel on one axle showed 1.6 ohm which works out to 3.2 ohm/magnet. So, right at the Lippert spec of 3.2, or very near. To add to the mix, the magnet with 3.6A showed 9.9V, which would indicate a resistance of 2.75ohm. Somewhere there is measurement error so if I ever get the Fluke meter I'd like, I will have to verify.
Also measured the voltage at the pin box junction, 11.65 volts, so there is already quite a bit of loss by the time it gets to the front of the 5th. Voltage on my scangaugeII while idling showed 14.3 so there is a 2.65V drop between the front of the truck, through the controller, back to the bumper, through the harness for the bed plug and through the 7-pin pigtail on the trailer. I tried plugging right into the bumper 7-pin and gained 0.25V but I don't want to have my wire draped over the tailgate.
Cleaned the brake shoes on the bad wheel with solvent again and reassembled. Magnet adheres to a steel plate with authority. Wear surface looks like it not yet worn completely flat so may need some more time to seat. It's hooked up and ready to head out tomorrow for another 3hr trip. I'd be happy if it will at least lock on gravel after all this. Assuming a proportional relationship between electromagnet force and braking power, it should work out to around 10% gain on the trailer axles.
