What to do under the dash besides this?

Jim Kueneman said
I would also contemplate replacing the harness if you have it that far down. The crimp fittings were never made to last 50 years, many of them are likely high resistance now. The dangerous ones are the ones that are high current (ammeter, AC clutch, blower fan) and get high resistance. You can get the AC and Main harness for for the '73 from Year One or Classic Industries (both M&H harnesses). The main harness is NOT cheap but I always bite the bullet and replace them.

This harness has a white connector under the steering column from ignition switch that has been known to melt down. There's a white one out in the engine bay that will melt down too. Crimped wire terminals both sides of those.
Any of them might melt down the connector to headlight switch. A new wiring harness renews only the female side of most connections which might not be a cure all.