I have a '96 F250 with Prodigy brake controller that is hooked to plug under dash. I have noticed the the 4-ways will activate the brake controller when a trailer is hooked up. Also I noticed that they will unlock the torque converter(just as if hitting the brakes) if turned on while driving. Is the the nature of the truck or is something wrong?

 

It's been a while since I pulled a trailer and used the 4-ways, but IIRC the P3 in my '90 F350 does the same thing. Not sure on the converter, mine's on a manual switch...

 

Have a look here: etrailer.com | Trailer Brakes Pulsing With Hazzard Signals On 1993 Ford F-250

A pulse preventer should be what you need.

 

Eric, so basically they wired up a diode in the factory brake lights wiring to prevent voltage being fed back though it to the BOO switch and the controller... Good idea, I'll hook up to my friend's trailer today and see if I really have the issue and if I need the diode too.