Troubleshooting dim Driver's side top light -- 86 suburban

[Ogre]

Hi y'all.

I have an '86 GMC Suburban.

The top light on the driver's side is extremely dim when operating low-beam. It seems alright in high beam, but I need to check it again tonight.

I've replaced the bulb, and re-done the ground wire, but haven't been able to fully trace back the orange wire (I'm assuming this is the low beam positive power).

I have this wire coupler at the firewall where I can trace the wire to, but beyond that I'm at a loss.

Thanks!

Roger