No front flashers '06 T800

Please forgive me if this seems long-winded. I just want to make sure all of the information that I have is available to diagnose.

Yesterday one of my drivers called me to tell me he was having lighting issues, it was pouring down rain and he had already been running for about 6 hours. I traveled out to him because what he described didn't make sense.

When I first arrived, all marker/clearance/tail lights were working on the truck and the trailer.

When the 4-ways were turned on, only the lights on the back of the truck flashed. Fender lights and trailer did not flash at all. I disconnected the trailer to isolate the truck. I had the same issue, no flashers on the fenders, but the rear lights on the truck worked.

Driver then stated that when he was still hooked to the trailer and pressed the brake pedal, the green arrow on the dash for the left turn would light up. I plugged the trailer back in and had him press the brake. Sure enough, the left side flashers on the truck turned on solid.

I checked at the gooseneck to trailer connections and found a poor repair job with a lot of exposed wires. I repaired this by trimming the 7-way back and installing a new 7-way plug. I then used my test box to check all of the lights on the trailer. Everything was back to normal for the trailer. I plugged the truck back in and tested the flashers again and still the same thing happened, no fender flashers and no flashers on the trailer either.

The truck is now the issue. All lights work when they should except the fender flashers (and the trailer flashers). They don't work with the 4 way switch, or the flasher stalk. I used my power probe to apply power at the harness plugs to each fender and confirmed that the lights still work on both the clearance/marker side and the turn side. I have an extra turn signal stalk so I just plugged it in to test and nothing changed. There is one relay for the left, and one for the right flashers. They both "click" on and off when the 4 ways or the turn signal is on, but still no power to the fender lights.

The driver said it all occurred at the same time and I am just drawing a blank here.

I have checked all of the fuses/circuit breakers and none of them are labeled as flasher/blinker. I've pulled every one of them that may have something to do with the flashers and all test good. I'm stumped. Is there something else I should be looking for? Thank you in advance.

TL;DR: Fender flashers and trailer flashers not working but rear of truck is.

 

Ok, so behind the dash, I can unplug the relay and send power to the lights. I get the flashers on and I also get power to the 7-way plug. But if I power the relay from the stalk switch the relays will click on and off, but power doesn't go through them. I followed the harness back to 6-wire socket and found that there is continuity between the left turn and ground, and the right turn and ground. I'm going to follow that plug to the firewall side to see if I can locate where my short is.