Strange electrical issues with my '72 Dodge truck

I'll wager that the headlights and/or dash lights have been run off the same circuit as the starter so it's overloaded them when they're on. Think parallel circuits.

I'd run the headlights off a separate relay and see if that fixes that problem and if not, it's still a worthy upgrade in it's own right. @crackedback has kits but not sure if they do trucks.