could this be causing an issue?

67Dart273 said
I would bet you money it DOES

66plyValiant said
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

67Dart273 said
Found this wiring diagram for a 79 over at MyMopar

http://www.mymopar.com/downloads/79_Dodge_Truck_Wiring_Diagram.zip

In the drawing of the 79 cluster below, my horrid photo skills circled the 3 VL terminals. I think I got it right side up this time, LOL

thanks guys! glad to be wrong. lol. how do I test it/find a new one?

RedFish said
A bad limiter can prevent the gauge from going to full. Then a saturated float can also.
As for it going to empty... Does the needle return all the way home at switch off ? Empty isn't all the way home , empty is the first hash mark.
Different conditions equal different problems.
Hope this helps

it returns to the empty mark at off. so it doesn't return home