Engine surges

V8 Four Wheel Drive Automatic 89'000 miles

Engine surges in time with the blinkers or the four ways, I can hear the fuel pump surging with the blinkers. Truck running taillights are very dim when they shouldn't be on at all. I cleaned all grounds to frame connections at fuel pump and at rear of truck, also checked wire harness from front to back, checks good. Replaced headlight switch in dash also.I seem to be getting low voltage on my test light on the burnt wire. My next check is going to be the turn signal switch. Any other ideas? Also if I unplug the rear tail light harness the truck wont start?Thanks for any help