Running lights, dash lights, and radio not working

I recently installed an aftermarket radio to my 91 b2200. I wasn't getting power to my red wire so I hooked it up to my illumination wire and it worked fine as long as I had my running/head lights on. It's been fine for a month or two, but all of a sudden it shut off on me when I was driving. Now my running lights, dash lights, and license plate light don't work along with the radio. I've looked at all the fuses under my dash by my knee and the fuses under my hood by my battery and they all look fine to me. (I'm no expert) Can anyone explain to me what I need to look for and do? Dumb it down for me please and walk me through it. I really don't wanna tear apart my whole truck trying to figure out the problem.

I can tell you this; my dome light, idiot lights, blinkers and head lights all work. The running light bulbs are fine because they come on when I brake for some reason. Don't care about that though.

Steph - there is a fuse for this circuit, in the fuse box in the dash near the driver's left knee, called "TAIL", 10 amps, but I don't think a bad fuse is the issue. I'm guessing that the headlight switch contact that operates the front parking lights, the taillights, and the instrument cluster lights (and in your case, the stereo) is bad, all are on one circuit. So the headlight contact still operates as it should. That exact same thing happened in my '88 B2200 4 years ago, and I wired in a toggle for the parking lights, the taillights, and the instrument cluster lights, so I had two switches to turn on, and turn off the lights.

Just last week the low beam contact in that headlight switch went out, so I swapped in a used headlight switch into my combination switch, and now everything works like it was 1988 again.

So yes - your dome light, idiot lights, blinkers and head lights all work - they are on a completely different circuit.

To troubleshoot, you need to have a DC test light, or a multimeter with a ohms scale or beeper, and a 0-20 volt DC scale. Specifically, if you test the headlight switch with the harness disconnected, you should have continuity between the BTN and TNS terminals with the headlight switch in either the "parking lights" or full headlights position. Of course, I'm assuming that you have access to the service manual to know which these are, and that you are able to remove the steering wheel and the entire combination switch.

I checked last week, the headlight/turn signal part of the combination switch is available new for about $70-$90, likely would need to be ordered (e.g. Autozone); there are two versions of the headlight switch, so be careful: there's a 4-terminal white one and a 5-terminal black one.

Anyway, for the stereo, doubt it pulls enough amps to have blown that TAIL fuse, but certainly check that with ohmmeter (when pulled out of fuse box) or with multimeter when headlight switch is on and fuse installed (check BOTH sides of the fuse). I wired up my stereo to a different place in the fuse box using a fuse tap, used a circuit that was on when ignition was running; that wire should also have an inline fuse in it to protect the stero (but that's not bad in your case, because that inline fuse going out will not affect your lights).