1980 k30 fuel tank wiring

[80crew454]

Hey guys I'm a new member to the forum but have been looking on here for a long time and first off would like to say thanks for all the great info and tips you guys rock.

Now for my question I have duel tanks on my k30. There are 4 wires that come out of my firewall and down the drivers side frame one wire(can't remember the color)goes to the driver side sending unit then the next three cross over to the passenger side where the second wire goes to the passenger side sending unit the third wire goes to tank selector valve. Here's where I get lost the 4th wire (pink I believe) goes back up the passenger frame rail across the back of the transmission and appears to go into the main wire harness block.

Is this a power wire? If so why run it all the way down bolth Frame rails and back up it appears to be factory wiring

Thanks for any help