On my 86, there are only 2 wires from the senders, no separate wire for the ground. So one must be ground.
There is a Blue/yellow from one thank, and a Yellow/Blue from the other. these go into the FSV. When you flip the Dash Switch to change tanks, then the Yellow/White wire out of the FSV runs up to the Dash switch, and into the big plug in the instrument Cluster for the Fuel Gauge.
I just replaced all my "O" Rings and return Hoses yesterday.
Looking at your engine picture, it is plumbed exactly line mine,
except I removed the hose from the Filter to the first Injector on the passenger side. There was a Ford TSB on removing it. Think there was a problem with it early on. Haven`t ha any problems with doing it.
At rear of the engine where the return lines come together, there is a hose that connects to that block and runs down the back side of the engine. That is the return to the tanks. Think it is 5/16".
I can`t tell if yours is blocked off, don`t know why someone would do it.
From under the truck, I think it is a grey plastic fuel line that comes along the frame, then runs up the Firewall to that block.
Some where there is a rubber hose connected to it.
I didn`t replace this piece yesterday, so not sure how the plastic/rubber is connected.
You can buy the Viton "O" Rings from McMaster-Carr size 111, in a bag of 50. use to be around $10. Now with Joe`s cut in the deal not sure what the price is today.
I used the same return caps, just cleaned them up, and bought some Gates rubber hose from O`really`s the proper size for the Caps, and used the same Spring Clamps.
When you do pull the caps off. Be sure to remove at least one of the Vibration Clamps off the Hard Lines. This way there is more springy give to the Hard Line W/O bending one. Bend/tweak Injector Line, and/or the posibility of cross threading the Cap Nut.
Be sure to replace the Vib/Clamps.
I fought the 2nd one from the front on pass side yesterday seemed like an Hour trying to tweak it back into linement.
Some ham ****** prior owner/s messed it up, and I have had it off several times. This time the S O B was stubborn.
EDIT: Another dirty word blanked out...
fis ted, there ya go
Goat