my left turnsignal does not work when the headlights are on it works with them off or with just the parking lights on wut when the headlights are on it just backfeeds through and lights up the dash indicator. anybody know what to check, i checked the bulb to ck for bad filament but bulb is good. this is on my 87 firebird.

 

Check the grounds at the lamp socket.

 

it works with the parking lights on. but when the headlights are on it is dim also the headlight is dim also. where does the ground for the headlight go?

 

found it, it was a bronen groung behind the battery.