Wiring headache

[HeavyK20]

Just bought a 1978 chevy k20. I knew when I bought it the tail lights were not working. I went home checked fuses all good , checked bulbs and they were good. Tested for power at the rear and came up with none. I don't know much about electric and was wondering if someone could point me in the right direction. Maybe a new rear wiring harness? Where might I find one and how much?

[PromiseKeeper]

there should be a connector right behind the rear bumper that pulls apart. Get a test light and see if you have power to there. Don't be hasty in getting a whole harness. Be patient and track it down. Most likely something simple.

[Blazin]

The tail light harness plugs into the bulkhead connector under the hood in the fire wall, at the back side of the fuse box also. Take the bolt out of the center, and all three harnesses unplug from it. Ones for tail lights, ones for nose lights, the other for the engine harness. Check the one if its still there behind the bumper first though and see if it has power that far back. It is the bed harness that plugs into the frame harness that runs the length of the truck, and plugs in under the hood. Allot of times with these older trucks someone will cut that connector out, and butcher the two harnesses together. Or do a crappy job installing trailer wiring!

[Camfirchev]

If I remember correctly. Your brake light signal from the the brake light switch goes through your turn signal switch on the column, then goes out to the bulkhead on the firewall.  You might want to check your turn signal switch for a bunch of broken plastic parts along with the wiring going to it.

[slammed79]

I'd check at the rear plug and go from there, the rear section is only 4 wires in most cases

[bake74]

   You only mentioned tail lights ?? Does your back up lights, running lights, or blinkers work ??  If so then it is in your tail light wires and not the others.  If you have none that is a different story. (the following still applies to the tail light circuit only)
 In wiring on a vehicle always think of direction, power goes from battery, to something and then back to battery.  Next think simplicity, you said you checked at the back and you have no power.  First make sure you have a good ground, then unplug the 4 pin connector in back as mentioned and check to see if you have power.  ( 1 for brake/running lights, 1 for backup lights, 1 for left turn, 1 for right turn).  If you do check ground for back of truck and light bulbs/assemblies.  (I had one the ground went bad and nothing on the back worked right, it was like it was possessed or something)
     If you don't have power on any of them, then as mentioned take the block off the firewall and check on the firewall side for power ( in the tech section do a search for wiring diagrams and find your truck ), if you have power at the block, first check for proper connection and if you got good connection, then it is in the wiring going to the back.   Replace or repair.  ( If you have no power at all in back, unless all 4 wires got cut, I would assume it is not the wiring).
     If you have no power at the block then it is in the cab.  Fuse block, steering column connection, etc. Sorry for the lengthy description, just trying to be clear.
    

[HeavyK20]

Thanks for all the help I started at the back lights had no power to anything. Went under the truck to the plug and cleaned the connection the best I could. I also traced it to the fire wall and cleaned that up too. Now all my lights are working. I went to the fuse box and pulled half of the wires out of it. I don't know what the he'll the previous owner did but it was a mess. Half of the wires went to nothing. I got all but one of my dash lights working. The only gauge that's still inop is my fuel gauge. When I start the truck it goes up between the two fuel gauges but isn't reading on either of them ? U haven't got a chance to figure it out yet but am guessing it isn't hooked up to the fuel sending unit.

[bake74]

     See, almost all your problems are solved, keep us informed about the other issues.