389 Marker light??

Follow the harness down, there's plugs right behind the bumper by the hood hinge. You'll find two 3-wire plugs, one is for the headlights and the other is marker/signal. Look for corrosion and check for power/gorund there.

 

Oh, my bad, 389's have a different set up, I was thinking of 379's. All the powers left/right are totally separate. Here's a schematic for your hood harness that should help figure out which wires are which.

 

Pull the back off where you access to change the headlight bulbs. I have seen the wires rub and get green inside the housing. Give each wire a tug and often you will find the issue.

 

Do you have 12v to pin 8 ? That should be marker power.

 

If you show power with an open circuit and it goes to ground when hooked up, it's a sure sign of high resistance. 99% chance that you are going to find corrosion somewhere in that circuit. Keep tracing that harness back looking for signs of chaffing/damage, check every plug. The 1st schematic was just the hood, hoping your issue was just up there. Here is the rest back to the chassis node and firewall connector.