Ok i also have a 87 F250 the guy i bought it from had the fuel pump in the front tank changed and the person who did it layed the wires from the back over the front driveline lol they rubed kinda thin and melted almost all the wires burned out the pumps and selector valve.
so
I changed the fuel tank selector to a manual one like the old dodges on the floor by the door.
put an electric carter high volume low pressure fuel pump on it.
but know i need to know where to hook the wires to be able to see how much fuel is in either tank so I have 4 wires one switch and no clue lol.
I need a wiring diagram or some one with a clue to give me some insight lol.
I have already rewired the lights except for the backup wires.
thanks for reading and as i said any insight will help.

 

I don't know if your 87 is the same as my 88 F250, maybe someone can confirm if they are the same. On my 88 F250 the wires going from the fuel tank forward are:

Y/LB 675 Rear fuel tank sender unit
DB/Y 673 Front fuel tank sender unit
BR/W 789 Rear fuel pump
PK/BK 787 Mail fuel pump (high pressure pump)
R 786 Front fuel pump
BK 57 Ground - Goes to S807 to G801

These wires go to a 12 pin plug on the left side near the brake master cylinder (under the hood) then go a big round 53 pin connector through the firewall.

Good Luck
Jerry