I did not disassemble the dimmer switch.
Interestingly, when I clicked the dimmer switch on and off a couple times, the driver side light became less bright.
The wiring in the truck overall is remarkably good. The insulation isn't cracked and flaking off and the wires are flexible. When this first materialized I swapped bulbs side to side with no change in results. Driver side worked on bright. So it seems that both bulbs will light up.
