My friends 1997 F250 7.3 auto trans stopped working the other day. The truck will not shift into gear and the brake lights won't work. The fuse for the brake lights keeps blowing. We pulled the trailer harness and plugged it back in replaced the fuse. Brake lights do not work and fuse blows.

 

short somewhere between the fuse and the tail lights. it needs to see brake lights before it will unlock the shifter. start tracing wires its not gunna be fun.

Diesel Rod

 

Could it be the relay?

 

Try leaving the trailer harness unplugged. If the fuse still blows, there's probably a short in the trailer wiring harness that goes from under the hood to the back of the truck.

 

Trailer harness has been unplugged. No brake lights and no shifting.

 

Which fuse blows? Does it only blow when you apply the brakes?

 

I will find out tonight which fuse blows. And yes, the fuse blows when you apply the brakes. I think the first think to do it figure out why the fuse blows with runs the break lights. This will help solve the no shifting at start issue.

Could it be the shift relay needing the brake lights on to shift.

 

Will the truck come out of park? If not then yes it needs to see the brake application to shift out of park. If will shift out of park just no go into gear it still could be related.

 

Fuse #13 is probably the one blowing. It controls the Hazzard Flasher, Truck brake lights, Trailer brake lights and Shift interlock solenoid. Something is causing the fuse to blow for sure. I've had the trailer connector (male end, one attached to vehicle) wires come loose inside and short out.

 

Yes, the truck will not come out of park.

 

The is a solenoid that keeps the truck in park unless the brake lights are on. If the brake lights don't work the truck doesn't come out of park.

There is a work around. Before starting the engine turn the key to the first click. Now move the shifter to N. Start the truck. You're fine until the next time you put it in park. But be careful, your brake lights will not be working!

 

not sure if its the same problem but...
I kept blowing the upper left fuse (#4 I think it is) when I was making the trip back from florida...my taillights, trailer lights, dash lights all went out....But turn signals, and flashers still worked.
It only happened to me when I had my trailer hooked up.. I guess there was a short somewhere n the trailer wiring...after I re-did the ground, they worked flawlessly

 

Found the problem. Cut wire in dash/column.