Blinker issue

If your running lights work it is not a ground problem, turn on the head lights
and see . It is an 1157 bulb one socket 2 functions , if you're not grounded you will have no signal light and no running light. Most likely a shorted wire.
May also be cuircut board in your dash . I am having a simular problem.
left rear signal light not working and when I turn on the high beams
the dash flasher indicators change sides. pulling my dash Sunday.
Cheers.