My turn signals, brake lights, & flashers have stopped working. I have replaced the fuse 4 times with correct size fuse and it has solved the problem temporary....maybe for 5 miles of driving. Them the fuse blows again. Auto shops cant diagnose the problem with a diagnostic. Any suggestions on what might be the problem. I'm thinking a short somewhere. thanks for the help

 

you have a short somewhere, i suggest going over all the wiring in the back of the truck and wiggling the wires until you can find where its blowing the fuse, check the connections at both tail lights and 3rd brake light. i've even seen a light bulb blow fuses if they blow just right the filament will short to ground and blow the fuse. if you still cant find it i suggest unhooking left and right tail lights, and 3rd brake light one at a time and drive around a bit to see if it blows

 

What he said. Start unhooking parts of the circuit until you figure out which part causes the fuse to pop.