Thought my tranny was junk, turned out to be trailer wiring

[Bestroken]

This is more of a relief post and possibly a heads up to others. I thought my tranny had problems. Drove 10 miles to get my trailer to pull a dodge home to my shop (LOL), every thing is fine. Pull the trailer 15 miles to get the dodge, and the whole way there, my 96 f-350 convertor is locking and unlocking. Tip into the throttle, convertor locks for 2 seconds, then unlocks, then tranny free wheels when I lift out of throttle all the way. So after getting home with the dodge, Im worried about my truck. Turns out the trailer lights were not working correctly, and Im assuming feeding back current to my brake switch, causing all of the convertor problems. Unhooked trailer, and tranny works great!! Who would have ever guessed trailer lights would screw up my tranny??

[JSchuricht]

When you press the brake the converter unlocks. Your probably getting some feedback on the brake lights. Is your trailer electrical jack factory or something spliced in?

[Chop]

Sounds as if the trailer ball could have been your primary ground for trailer lamps,kinda giving the off and on syndrome .I seen this with many a boat trailer ,lamps back feeding thru the other filament

[madpogue]

Similar issue as when the cab-roof center stop light is out.

And yeah, the old ground-through-the-ball thing is totally old-school. Good idea to confirm that the ground pin on the connector is really connected, on both sides.

[Bestroken]

The trailer plug has been attacked by the weed eater too many times. Time for all new wiring. My dads trailer, every time is use it, I have to patch to wiring together to get by.

[Fordman247365]

Just a heads up, my ground for trailer is on my frame thru the plug and out to the trailer frame and a tap of the pedal also unlocks mine, maybe they way the factory wired in the towing package?