I can't see where manually applying full brakes with the controller will cause a Jack knife. If you lock up the trailer brakes, your just dragging a huge chunk of dead weight.
I have had to do it a few times when a rude driver decides they need to pass me at 75 to make the off ramp 100 feet ahead. I no longer do it, I just maintain speed through and apply full TRAIN HORNS
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2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.