The original dimmer switch wheel uses a potentiometer that will notoriously often stop making good contact and make the dash lights just not work. That's why it was likely bypassed. I remember seeing a video of the dimmer switch carefully being taken apart and the oxidation removed from the contacts to make it work again. There's a product that you can brush onto electrical contacts that works really well called DeoxIT: CAIG DeoxIT D100L-2DB Brush Bottle 7.4 ml (parts-express.com)
If the box you're talking about is an aftermarket part with no Ford marking or Ford #s then it was just likely bought with that rigged up universal dimmer knob. I'll bet that it doesn't work anymore. You can bypass it completely and give it the full 12v. It looks like someone did a real low budget wiring rig job in your car. I would restore the wiring back to how it originally was from the factory and just fix your dimmer switch.
