What is this thing

Lower piece is a "condensor" or "radio noise suppression cap" see http://www.allpar.com/history/mopar/electrical2.html about halfway down.

If you retrofit to a solid state 5V regulator, you can pitch the condensor and the shoddy, 60 year old tech regulator for something that'll probably never die as long as you put a big enough heat sink on it. The link given earlier will not "bolt in" on a mopar, unless you're OK with just jamming those ring terminals down into some slots. It took me about an hour to wrestle the damn dash out, and about 5 minutes (4 minutes of waiting for my iron to heat up, two of those spent eyeballing a bag of capacitors to find an appropriate reading and figure out which lead was negative) to solder one of these in from "bare parts" in Radio Shack bags (about $15 total investment if you include a new spool of solder), and then a half hour to wrestle the stupid dash back together. If you check out the article, you'll see that the screw hole the condensor tab uses is the perfect place to mount the heat sink and regulator, it's about 18 inches of wire. You're honestly not buying much saved time with that kit.

I also took the opportunity of the dash being out to replace all the 194 instrument bulbs and their 5/8" 194-type black socket housings - the bulbs were $5/10 and the sockets were $10/10, and used some scotch brite and vinegar to "brighten up" all the connections around the lamp sockets. I then dabbed some dielectric into the sockets and onto the tab contacts. It's probably overkill but its cheap insurance against crappy flickery dash lights and mystery gauge waves.

One of my "main instrument harness bundle" pins was a bit wobbly so I put a plug on it to hold it straight and soldered just a tiny bit around the base, which seems to have stabilized it. Hopefully I never have to take this off ever again.