Blowing 20A Fuse to my Running Lights

I've been working on final bugs in my Duster restoration when a new one just popped up.All wiring harnesses were replace with M&H harnesses during the build. All electrical components were working fine. Recently, my turn signal flasher stopped working. I purchased a new one from Auto Zone and fixed that issue.
The other week I had the car running in the garage at night when I turned on the lights and did a walk around. I noticed that none of my running lights were working. I looked at the fuse block and saw that the tail lamp fuse was blown. I replaced the 20A fuse and checked again. Blown again! I removed the drive kick panel and pulled the plug to the rear harness. Replaced the fuse, and tested again. The fuse is blown again.
Headlights, turn signals and hazard flashers are working. All grounds had been gone over multiple times during the rebuild. Just wondering if anybody has any ideas or insight as to what else I should check. I have my FSM out looking at the wiring diagram. I hate electic Gremlins!!