As am I. What kind of Tommy Boy got in there and convinced people to buy their stuff after their brand became synonymous with dysfunction?

Oh, I resolved the issue.
I found that the sockets were corroded AND the contacts were pushed out of shape somehow. So, while I was probing, I was picking up zero current at the spots where the hazards should have been doing their thing.
I started swizzling the meter probes around and started getting voltage. So, I put the bulb back in and got nothing. I pulled the bulb out slightly and voila, light.
So, the connectors were just dirty and spread out. I'm cleaning them with alcohol and tightening them up by pushing with the tip of a file to bend them inward for more springiness.
Now I can retape all that stuff and bolt the trailer hitch pigtail back to the hitch. Huzzah.

 

Coolness. Some dielectric grease in there to prevent corrosion wouldn't be a bad idea either.

I remember, back in the day...... Jaguar owners were teased that they needed to own at least two, so maybe one would work, while the others were in the shop.

 

Yeah, that's a great idea to grease them.

I'm just glad it turned out to be so easy. On my scale of difficulty, soldering is easier than trouble shooting.

One of the problems I keep having is assuming I know what something does. The wild goose chase I was on was thinking that the lower lamp was the stop/turn, but it's a reverse lamp. So, hopefully I've learned my lesson to not work anymore on this truck without RTFM first.