Issues I've found several times over many years---people wire turn/park/marker lights incorrectly with power going to ground which then goes thru both filaments in the bulbs and then body of lamp to fender creating lots of current draw plus that then effects the flasher----------

get volt/ohm guage and dissconnect all wires to light, remove bulbs, check to find true ground and also identify which wire feeds which bulb filament-------

some of the overseas supplied bulbs have sloppy contact points on bottom and don't line up on the terminal in bulb socket---------

At least turn signals are usually light weight and don't need a --------------------