the Rear light is VERY dim (if it comes on at all), the front marker light doesn't come on at all. Drivers Side is Fine.

I'm savvy enough to fix it, I'm not savvy enough to know where to start.

Thoughts or suggestions?

FYI - I THINK the front fender has been replaced at some point, maybe a sign of electrical wires that were disconnected and fixed at some point??

 

Take the light out and check the voltage. If your not getting the right voltage trace the wires for a short or break.

 

The side marker lights have several soldered LED bulbs, some of which will burn out and make the light dimmer. I replaced a front driver's-side sidemarker light for the same problem as your rear passenger-side marker.

Check the voltage to the marker lights-- then replace the markers if the voltage is good. Aftermarket markers-- stock or blacked out-- are much less than OEM prices from dealer parts; AZ vendor dealer prices are in between, IIRC.