Gauge cluster wiring help

[Mike L.]

Today in preparation for a holiday trip east we bypassed the alternator on my '85 j10 and installed a new marine ammeter and external 75 amp shunt away from under the dash, everything works fine except when we pulled the panel out the oil and fuel wires became detached from the plug that goes into the circuit board, we've now got the purple oil pressure wire back on in the right place but no fuel gauge, there is 1 more wire (black or dark grey) that appears to have come out of the plug at the same time but it doen't seem to do anything. Anyone know what the color of the fuel gauge wire is and if this is where it goes. Really appreciate any help.
Thanks

[35sNoLift]

Howdy,
Not sure what color the wire is for the fuel guage. Can you disconnect from the top of the tank and check for continuity from the dash to sending unit? I know it would be easier to find a diagram but...