You probably found the problem. We kind of eliminated everything else.....maybe.
If you are not going to drive it anymore, just jumper the coil with a quick release method. If going to drive to work, bypass ammeter and rig a new 12V to switch. It will all get worked out when cluster removed/dropped at new harness install.
The harness install time effort depends on your time availability. A few days to a few weeks. It's a careful rip out of the old in a manner that keeps it in a "harness" configuration if possible for reference, save EVERYTHING. Then mount fuse panel inside firewall, probably upper left of left foot. Harness will have three basic harnesses, 1)front lights/engine....2)dash/dome and 3)rear tail/stop. If you have a turn signal switch on column, that's a separate easy effort.
It's your truck, so do what you think is best. I'm just giving my too sense. Let me know before buying something.
your generator is either a genuine 12V gen, a converted 6V or a 6V with a 12V reg.
