Tail Lights/Park Lights Problem

I'm having a problem with my tail/parking lights not working. Is there a common problem where the park light wire short out in these trucks? It is in the main harness before any plugs. I figure it is an old brittle wire that finally broke because of time and the shitty ride. Here's what I have done so far, but I thought that someone might have had the same problem that is common. Next step is just to rewire the lights.

I was driving the other night and my dash lights went out, I pulled over and checked the fuse and it was blown (tail fuse). Took the cig fuse and tried it, as soon as I put the park lights on it blew again.

So today I pulled it in the shop and unplugged every light including front grill park lamps, tail lights, gauge lights, dash lights, etc. Put a fuse in and pop, checked the line and theres still a short. So I know that it is in the harness before any lights or plugs. The back of the fuse panel is tight (wire secured).

Thanks.

The harness for the rear lights exits the bottom center rear of the cab.Over time the harness may have frayed causing ur short.Check there first.BJ