Well here's my total problem...
I have a digital dash and the fuel gauge always says full. All the other gauges work fine but the dash flickers greatly and even goes blank as I drive down the road and my heater, while set to "on", comes on and off in conjunction with the dash flicker along with the headlights dimming and brightening and the turn signals only work when the headlights brighten, dash lights are on and heater is running. They all seem to work, work less or not work all at the same time. It's flicker city. What could possible cause all these things to work or not or just not all the way, (lights dim, dash dim, heater runs low), all at the same time?

 

Well the gas guage not moving accurately is common in these trucks. Ive spoken to a few owners that have the same problem that I do, it reads full until way past half a tank then drops off really fast. With yours not reading anything but full I would suspect that the float in the tank is stuck, or if there is a fuel level sending unit that its on the fritz or come unhooked.

For the dash you wouldnt hurt anything by taking it apart and checking the connections on the back for looseness of maybe it has a broken wire connector thats flopping around some. See if you can chase the ground wire that should be black or brown from it to where it grounds to the chassis. Also check the fuses for tightness and rust on the connections at the fuse board.

I would also check the battery terminals for tightness and corrosion that looks like white or blue powder build up seeing as how it seems to affect every electrical component on your truck. And test your alternator as well, you can do this with a multimeter - 14.4 volts running is prime! Anything more or less and you have a voltage output problem that can be fixed with a cheap rebuild kit. They are easy to install and cost about 30 bucks. They have new berrings, springs and brushes, and a voltage regulator. The hardest part is getting the pulley off the alternator. Use sockets that match the size of the outer berring surface to drive them in and out with a mallet or press them in the vice. Sometimes the voltage regulator requires soldering in.

Having a tube of Dilectric grease for putting on the connections when you are hooking stuff back up never hurt anyone either. Its about 8 bucks for a tube, and great for putting on connections to keep water out. I use it always on lightbulb connectors, and anything else that looks like it could use some of this stuff.

I hope this gets you started, and more of the members will chime in here today with some more help for you.