I have an 07 softail Custom FXSTC. The left front blinker works and when at a stop light the marker light is bright. Once I start going the light dims almost to where no light at all but the blinker works fine.

Thoughts?????

 

It's one of two things going south.
1. Stator
2, Altenator

 

Being that it is only one light dimming I would check the wire for the marker light on the turn signal and see if you are getting a good or intermittent connection to power, seems like an intermittent connection because of vibrations will dim it. Start with the bulb though, filament may be the culprit.