Can someone tell me why my driver side rear running light is dimmer than my passenger running light?

 

Different bulb maybe, resistance in the wire

 

Which running lamp, the tail lamp or a marker lamp on a fender?

Somebody could have jammed the bulb in backwards or you could have lost the ground to the lamp so it is backfeeding through the turn signal filament.

Do both turn signals work?

 

yea everything works. just the driver side running light is not as bright as the passenger side. and its the tail light.