I found a stop/tail light wiring harness on Brothers website
http://www.brotherstrucks.com/prodin...number=WH22075 but it is not all that inexpensive. I went there because it was easy to get to what I wanted to but be sure and check different vendors sites for prices. If one of these trucks ever towed anything the stop and tail light wiring is often hacked up in that area. There should be a harness with three or more wires running down the inside of the drivers side frame rail to a plug in the back crossmember where the harness for the tail lights and side marker lights plugs in to it.
A lot of guys on here don't build or restore their trucks with plans to haul anything except a cooler and soft duffel bag so you will get mixed opinions there. My truck works for it's keep so I've been thinking about some but they will go inside the bed if I do.
I'd remove the seat first and then take the bolts holding the straps for the gas tank out and unhook the line coming through the floor to the tank. I'd do that first along with unhooking the wire for the gauge. Some guys take the clamp to the hose to the filler neck loose and pull it off the tank before removing the tank but I pulled mine with the fller neck on it. It was a fight though.
I'm not sure on the bolts to hold the bed on but think there are about eight. I'd pull it off to paint the cab and front of the box if it were mine.
Gas gauges are beyond my scope as I haven't had an operating one on either of my trucks for over 30 years. you may have a ground issue though and I'd check that first.
On the back glass rubber, if you look at the outside of it close you will see a line down the middle of the rubber that goes all the way around. That is the seam for the locking part of the rubber. If you take a skinny old worn out screwdriver with a well rounded off end and maybe an ice pick to get it started and start at the bottom corner you should be able to lift it up an release the tab. you have to work your way all the way around with the screwdriver or tool of choice and then gently push the window out and back. For my money I'd cut the rubber and buy a new one if the old one is hard as they quite often get torn up anyhow. Wes at
www.classicheartbeat.com sells some nice window rubber that I like.
On the headlights it is most likely the dimmer switch I put one in my 71 this afternoon. Two screws hold it in. Get the NAPA Echlin DS115 and if the harness going to it is bad it's number is SC115 I had to put both on my truck today.
You can unplug the switch an with a jumper wire go from the center slot to each side and turn the lights on and see if both sides work. If both work it's a bad switch if only one works you may have other issues.
Removing the core support depends on how fast you work and how crusty the bolts are. I'd expect to spend most of a day unless you work pretty fast.