What color is ground? + Fuel gauge question

[DuckAholic1]

87 R10 350 TBI Duel tank... Having a brain "fart"..... what color is the ground wire for the sending unit/units? Also have a gauge problem..
1) When selector switch is on left tank, gauge reads just above 1/4 when tank is full.
2) When selector switch is on right tank, gauge reads over full.(needle all the way right)

Bottom line I need advice on where to go from here. check grounds, replace both sending units, etc??

[Irish_Alley]

#1 i would think sending unit since the gauge does move when you switch tanks
#2 is prob because of a open circuit or poor ground. 
your grounds should be off the sending unit and attach to the filler neck
Gauge test
i did look here for your wire diagram but couldnt find it. maybe im not looking in the right spot idk
Truck manuals

[DuckAholic1]

Thank you, Irish!!

[Drizzle]

I had the same issue and found the cause was the sending wire.  You know the wire from the selector valve is good cause the other tank shows proper level.  So it's leading to either the group or sending wire from the tank itself.  The ground wire on my truck was bolted to the frame visible between the cab and the truck bed.  Pain to get to.  I believe because your gauge shows way full it leads to the sending wire going to the selector valve from the tank in question.  Cut off old wire and splice in new wire temporarily to give it a try.

[DnStClr]

Here's a pic of a pump I replaced. The ground wire was black. It was attached to the frame like Drizzle said. It's the wire with the yellow terminal .


on edit- that's a pretty lousy picture isn't it?