[Longhorn Man]

Don't let electricity kick your butt. You can't see water in a pipe, or exhaust in your muffler... but you know it's there.
Electronics are easy... especially at this level... this is simple stuff here.
You need 12 volts positive.
That's the + side on the bettery.

You need a conductor
That's the wire.

You (usually) need a switch
Ummm, yeah, that's the switch

You need a load
That's the light bulb, motor, blower... what ever.

You need a ground
That's dang near any piece of metal on the entire truck.

Clean/tight connections, no pinched/broken/corroded wires, a good Component... and a good ground.
It's really, almost THAT simple.

Something don't work, look for the obviouse stuff... or the most common stuff.
Taillights not working? Look at the fuse, the wires under the bumper where the traler harness has been installed over and over, check the ground. Those 3 checks fix 75% of the tail light issues.