Need help!
 

First off hello! I'm here for some educated help. I'm working on a f350 SD 6.0. Owners tail lights kept blowing the fuse. Owner then puts 25 amp fuse in and stopped blowing fuses but now there's no power. Ive traced wires back thru harness to the engine compartment found the connector plugs followed brown wires back to fuse panel and the lower connector on backside of panel has bwn, ylw. Tan/wht. Wires in it. Only has power to a couple of the wires out of over a half dozen... I can't find any burnt wires I did find a spot behind the aftermarket LED tailights that showed sign of short on body the sockets are bad but the brn wires are still dead. And ive cleaned ground on frame and swapped thhe correct fuse

What year vehicle?
Some fuses are powered by other fuses, so be sure to check them all.

Is the fuse that was put in oversized for F17 in the under dash fuse box? It was supposed to be a 15 amp? F17, 15 amp is what feeds the tan/white wire going to the headlight switch.

If that fuse socket is dead on both sides, check fuse 1, 4, 11, 10, 104, 37, 113, 40, 105, 602, 114, 8, 115, 6 , 12, and a bunch of others. It all those fuse sockets are dead, then most likely fusible link A or B have burnt in two. These are located off a junction block that leads to the battery +. These fusible links feed all those fuses.

If only that one fuse f17 is dead, and all the others have power, then I suspect the fuse box is burnt.

Fusible links A and B as shown in the attached PDF go on to power the portion of the fuse box that in turn powers the tail light fuse. Both fusible links are located in the wire harness coming off the battery on or around the drivers fender.