Got some time to do more checking. Looks like there is only 16 ga wire going from pin box to axles. Then there are short sections of 18 ga actually coming through the underbody and feeding each axle, as well as 18ga crossing through the axle to the opposite side. This seems really light to me.
Also, checked voltage at the bad brake(first splice) and it's 8.6 using the break-away switch (no truck). Battery was at 12.6 no load and 12.3 while the brakes were full power. Also checked it with a charger connected... 9.3 at the wheel and 13.0 at the battery. So, a solid 3.7V drop at the brake with the shortest run! I don't have a current clamp and I didn't want to cut wires and splice quite yet. I also checked the voltage at the rear axle splice and it was the same.
Anybody else ever check voltage at the wheel with the break-away switch? If you have battery voltage at the same time, that would be good info.
