my driver side, side marker, doesn't turn on when i flip on the headlights. however, if i signal left it works. another thing i noticed is that my passenger side marker turns on when i flip on the headlights and it alternate blinks with my front blinkers.

i've checked the wiring so nothing is cut or worn out. what else should i look for? and how do i setup the wires to do the alternate blinking?

TIA

 

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ttt