Running Lighst Fuse Blows

[AZSenza]

Hi all, Running lights were working fine, Last night, I hooked up the plug (7 Pin) lights came on then blew the running light fuse on my truck. (Truck has its own fuses for all trailer items). Truck wiring looks good, I suspect the trailer but where to start?

 

[BatDaddy1887]

Re: Running Lighst Fuse Blows

The first thing to check is the ground. Unbolt it and file it down to metal again and replace using dielectric grease. Check your fuse to make sure it is the correct amperage for the lights. Sometimes the wires get frayed from normal driving where the wires might rub against metal, check the entire system for frayed wires, be very thorough in this part as the smallest wear point could cause a short. If the wires are old and hard, they could have simply broken, you would need to re-do the entire wiring in that case. Check your bulb sockets, while you're in there, file or sand those down as well and again use dielectric grease on all connections, even in the 7 way plug and socket. Use a volt meter to test each wire. Good luck.

 

[Jetwash]

Re: Running Lighst Fuse Blows

Its a short to ground. To clarify, you said you have fuses for the trailer wired into the truck? Are you confident that you can determine the short is in the trailer wiring, or do you need to go back and isolate the truck from the trailer?

You can double check by running a hot lead to the plug from a battery. Ground it back to the battery. If you dont put a fuse in the circuit, the wire will get hot and it may spark back at the battery post. You want to avoid sparks at the battery since you cannot tell if the battery is gasing and therefore liable to explode. That is THE reason you always hook up the positive first and then hook up negative. To remove cables, remove negative first and then positive. First on-last off.

Just follow the hot lead all the way back to each light. Chances are its been rubbed raw on a burr or a fastener. Any work you did recently is a prime candidate.

 

[AZSenza]

Re: Running Lighst Fuse Blows

Thanks, Yes, the fuse in the truck is correct, it WAS the original, I've used it fine for 5 years. The trailer IS the unknown. I just rewired the plug, thats the first place I'm going to look. It was working for about 10 min, I unplugged, then plugged back in, seconds later it blew. I'm guessing a wire in the plug shorted out. Thanks. I'll let ya know

 

[AZSenza]

Re: Running Lighst Fuse Blows

+++UPDATE+++
Took the plug apart, inspected connections, inspected truck, inspected fuses, checked resistance and voltage, checked grounds. Hooked up trailer-everything works, for now. I Hate it when I dont find the problem. I'll keep looking but at least its working for now.