On my setup, the P3 gets turned on via a touch of the Suburban's brake pedal
A 'touch' enough to turn on the brake light switch, but not enough to develop MC pressure, that would get the TV's brakes involved
That touch tells the controller to send voltage to the trailer brakes...at the preset, which is NOT 100% voltage
The manual lever tells the P3 to send full voltage to the trailer brakes. 100% braking is something NOT to do in your situation...nor lifting off the throttle
Have had the same situation towing from Tahoe back to The SF Bayarea...on a curve that is in the shade, so moist. I drive slow in the mountains and even then, this happens on occasion...just touch the TV's brake pedal enough to turn on the brake light switch and the trailer will have braking at the preset, which will pull the setup straight as the throttle continues to motor on
It is all in the setup...
