Fuel Gauge wiring location with factory single tank

[cerial]

Bought a 85 GMC 2500 4x4. 5.7, sm465, 208, SF14, 10 3.42 ratio standard cab 8'bed Yesterday. The truck was used as a airport truck then it was sold to a family who had it for 20+ years.

It runs drives and stops great. It has rust of course. But I really just want it for a deep snow winter ride. It has a few issues besides the rust that I will be addressing. One of those is that the fuel gauge does not currently work.


Now I will no doubt eventually do a 5.3 swap and run a back seat out of a 2017ish truck. But this thing runs and drives currently. This year I really just want to fix the floors so its not throwing snow inside and refresh things so it's not going to leave me stranded during a blizzard.

The sending unit on the drivers side is right between the cab and the bed and I can get my hand on the green and orange wires to see that they have been cut. I should be able to connect these to new wiring without dropping the tank.

Green is the ground and the orange is the sending unit from the looks of it. But looking around I can't seem to find what I am assuming is going to be green and orange or orange and white wires going to the gauge. Looks like they ran a new taillight wiring when a newer bed was installed and the harness from the cab back was removed.

Now I have a 91 cab and chassis R30 square and a 87 1/2 ton V10 square so I simply went up to the selector switch on the dash when going to single tanks on those. But this 85 does not have a selector switch.

So where will I find the wires coming off the gauge preferably without cutting into the plug behind the cluster. (worst case I do this)

Should I start behind the dash near the center of the dash? Would the gauge wiring be there?

I am guessing it would run from the dash down the passenger frame by where the old selector would be. Or with a single cab single tank it could be ran down the center of the cab. Even skipping the dash all together and running next to the speedo cable.

Before I spend hours searching and testing wires I thought one of you guys might know where to look maybe even if the colors change behind the dash etc.

Thanks for reading and any help in advance.