I thought they did away with running the wiring through the hinges on later years than my '86. I was under the impression they now use a pop out on the body at the top. Then go through an 8" to 10" rubber conduit in to the tail gate?

Must have lost a connection in my head!

It sounds like you have lost the ground on the license bulb holders via those wires.

I think the sewing needles should work except the wire strands they are touching are crappy. You probably are not getting in touch with enough to conduct. Plus the needle is steel.

The wire itself is made of several fine strands as they were trying for flexibility. It is a case of over thought engineering.

That made the wire frail at the same time, flexing metal work hardens it.
As the wire flexed the strands broke and the remaining conductors get hotter making up for their lost buddies. More heat more oxidation.
You heat copper and let it cool slowly it gets harder. It is the opposite of steel.
You heat copper and quench it to soften it.

On my '86 under the corner below the hinge beneath the vinyl head liner is a connector. You can replace the wire from there back by splicing and then plug it back up. You may want to remove the door or at least prop it up safely when undoing the hinge to work through it.

Just make wire longer. Put the splices and excess wire in the door or in the car.

Hope this help you some,

Phil