could this be causing an issue?

DarTT said
Nope. No voltage regulator on the dash. and my truck is a '74

I can bet money it does too, my 1979 does and yours has the same dash in it, its a 3 prong 5 volt regulator that sends on/off power to achive 5 volts

even our old A bodies have that, in your truck its behind the gauges on the printed circuit board