They normally don't go bad and if I recall the ford service manual instructs to clear the lines to the tanks and to also inspect the tanks for debris. I will never put manual valves in. I even am adding a second fsv with my third tank that is going in the bed. Also how do you switch the fuel gauge over?
For three tanks you have to have two six port FSV's and two Front/Rear selector switches. The gage circuit is simple, wire in a relay. The plumbing is a little more involved.
For plumbing.
FSV#1 is for Front/Rear Tanks. Source #1 Return #1 Source #2 Return #2
FSV#2 is for Bed tank. Source #3 Return #3 Source#4 Return #4
Source #1 and #2 outlet lines hook to Source #4 inlet, use a tee at the inlet port.
Return #1 and #2 outlet lines hook to Return #4 inlet, use a tee at the inlet port
Source #3 inlet just hooks to the suction of the bed tank.
Return #3 inlet just hooks to the return of the bed tank.
Outlet of FSV#2 source hooks to the 3/8" line running to the engine.
Outlet of FSV#2 return hooks to the return 5/16" line coming from the engine.
Original Frt./Rear selector operates in the normal way.
Second Frt./Rear selector should be labled #3 and #4. Selector has to be in #4 position to draw fuel from either Front or Rear tanks, when in #3 position, fuel will be drawn from the BED tank.
The fuel gage will operate in the normal way for Front and Rear tanks.
For the Bed tank FSV#2 connector is marked 1-2-3-4-5 or A-B-C-D-E F pin is not used.
1-2 or A-B is the motor to select the tank, 3-5 or C-D is the gage indicator from the tanks, 4 or D is the direct circuit to the fuel gage.
A relay has to be energized by the FSV#2 when the BED tank #3 is selected, a NO contact has to be in the 4 or D wire, and a NC contact has to be in the FSV#1 4 or D wire, the FSV#2 4 or D wire has to be spliced into the FSV#1 4 or D wire after the NC contact so it's direct to the fuel gage.
The 1-2 or A-B can be either Positive or Negative depending on which tank is selected, so when installing the relay, make sure it's energizes when the switch is in the #3 position.
When marked #3 #4 selector is switched to #4, fuel will be drawn from the Front or Rear depending on which tank is selected, when selected to #3 fuel will be drawn from the BED tank and the Front/Rear tanks will be blocked.
I hope you understand all of this.
It was confusing to me just to write all this, hope I'm correct. Took 2 hrs. just to type it.