Ron,
Sorry to see I guess that's you with the cast, be careful.
Easy enough to see if it using magnets or a big high wattage low resistance resistor. If used and it acts magnetic, magnets but I also bet that because it has 3 axle setting, that's 6 magnets that thing would weigh a small ton. I've sorta found a wire wound resistor that can simulate the magnet load if I wanted to build a dummy load to plug into my tester.
That's where I made mine different, heck had no clue these existed. Mine plugs into TV and then trailer plugs into my box and I'm seeing "rig" voltage and amperage values. Next week I have a chance to try mine on "volunteers" and plan to capture data to help build handbook of recorded data.
If you're bored and wanna get back into Ohms law I think between their video and knowing that EACH magnet is about 3.5 Ohms wired in parallel you can start to calculate the total resistance of the trailer brake circuit and get the old Ohm's law wheel going and created predicted values.
And for those that didn't spend time in class like Ron no, it's not 4 X 3.5 ohms = 14 ohms you'll have to calculate for resistance in parallel.
And agreed, between getting truck controller produces XX and trailer values are XX controller settings are XX and PWM is XX this can be a seriously interesting I've gotta know kinda topic.
That is a cool looking tool and looking forward to next data installment and get better soon Ron
Gary