[ImperialCrown]

Sorry I didn't see this until now. Check the bulkhead connectors at the firewall for signs of heat and/or corrosion. Many times I have found melted plastic and green terminals. Actually separate the connector halves (if you can).
The ignition switch is another problem area for developing this high resistance.

 

[MoparNorm]

See IC's post. This is a very common problem with both cars and trucks of that era, from about 1961, until the removal of the amp gauge and use of a voltmeter. There are several web pages devoted to the cure, (and maybe here at Allpar) but the basic issue is running the primary alternator feed through the amp gauge (and dash) before it goes out to the battery and various other components.
This generates a lot of heat at the connector which is prone to water, dirt and brittleness over time.

 

[53 Flathead]

Thankyou, it was a loose conection under the dash.