Yeah, just crack the window. When any 1 of the trailer tires locks up, you'll here it. Don't come to a complete stop. Once you here that chirp, let go, dial back the voltage a bit, accelerate back to 25mph, and try it again. You want the system right at the point that it's thinking about locking up.
With windows open, warm up the brakes first, with a few gentle, manual stops from 25mph. If you start smelling the brakes, that more than enough. If you set them while cold, they will be set too low, since they get more effective at moderate temperature.
When do the full apply, they really mean it. Apply it quickly to full manual apply. You are simulating what would happen when you do a full panic stop in an emergency. You want your ABS to keep the truck's tires from locking up, and you want the controller set for max braking, but without locking trailer tires.
thebrakeman ('70), DW ('71), DD ('99), DD ('01), DD ('05)
2004 Surveyor SV261T (UltraLite Bunkhouse Hybrid)
2006 Mercury Mountaineer V8 AWD Premier
Equal-i-zer WDH (10k), Prodigy Brake Controller