When checking for voltage you can check across the bulb contacts with the bulb removed. But also test each contact against a body ground. This can tell you if you have the supply voltage but no ground on the bulb side.
OK. I need to ask the OP. The first picture in your first post shows the festoon bulb installed behind the heater control facia. Is that a picture of your truck in your current situation. It looks like the filaments are glowing, indicating both that you have some power and the bulb is not...
The parts diagram does show a 12v bulb for that application for the HJ61s I looked up. I don’t know the OPs exact model variation though.
The 12v use is also supported by the wiring diagram that shows a resistor for the HJ61.
The OP says he has no power coming to the light bulb. He would be...
If you checked the connector for power (voltage) against a good local ground point, and you did not have power, then the wire ground may not be your issue. With no power coming to the light you need to check things between the batteries and the light, like fuses, etc. But since all your other...
I looked at this wiring diagram and decided I don't know how to interpret it, especially the part after the instrument lights where wires go both to ground and to ground via the Rheostat (dimmer). The ground for the HVAC light goes to ground bus "d" which is under the front right pilar. What I...