I just repaired about a foot long section of the right tail / parking light harness on my 89.

Somebody, apparently pulled the overflow tank out and then put the tank back in 
allowing the harness to drop down into the slot between the muffler shield and the body. 

The one foot section was completely melted solid, it was actually working for some of the circuits. I kept blowing the fuse for the parking tail lamp which made me find the problem. 

When you open your license plate door you should see the harness running across the front of the bottle. If its UNDER the bottle. You will cook the wiring. 

Doug