Dash Mounted Fuel Selector Switch

[lewain]

I have purchased a new electric fuel valve to replace the stock valve located under driver seat.
My question is: On the back of the fuel selector switch on the dash there are 6 connection points. Top 3 are tank connections with the middle going to the gauge.
Bottom connection points from what I have read; center tab is for 12v and one of the outside tabs go to electric valve. What is the 3rd tab on the bottom? Is it energized when the selector switch is flipped to the other tank so that you choose which tank you to open the valve too?

 

[.94 OR]

The switch should be a double pole single throw switch.
The upper set of 3 creates a ground circuit to either fuel sender/float in the tank then grounds next to the tank.
The lower set of 3 should be set up similar. You would supply power to the center (ideally), then run the feed to the electric valve for the auxiliary tank so the switch is naturally "parked" for the main tank to operate. The pole on the switch that would correspond to powering the switch for the main tank would not be used as the valve would default to this setting for most of its use.

 

[jamesroney]

The switch should be a double pole single throw switch.
The upper set of 3 creates a ground circuit to either fuel sender/float in the tank then grounds next to the tank.
The lower set of 3 should be set up similar. You would supply power to the center (ideally), then run the feed to the electric valve for the auxiliary tank so the switch is naturally "parked" for the main tank to operate. The pole on the switch that would correspond to powering the switch for the main tank would not be used as the valve would default to this setting for most of its use.

The factory switch is double pole, double throw. (DPDT) It has six terminals with two isolated circuits.

Totally agree with everything else.

 

[lewain]

The switch should be a double pole single throw switch.
The upper set of 3 creates a ground circuit to either fuel sender/float in the tank then grounds next to the tank.
The lower set of 3 should be set up similar. You would supply power to the center (ideally), then run the feed to the electric valve for the auxiliary tank so the switch is naturally "parked" for the main tank to operate. The pole on the switch that would correspond to powering the switch for the main tank would not be used as the valve would default to this setting for most of its use.

So, if I wanted to naturally “park” the auxiliary tank I could just use opposite pole. Correct?

 

[.94 OR]

You would want to plumb the fuel switch so that the tank you would primarily use is in the "open" position, meaning the valve does not need power to energize that port. Then the dash switch would trigger the valve and the gauge to activate the other tank. Hope that makes sense.

 

[jamesroney]

You would want to plumb the fuel switch so that the tank you would primarily use is in the "open" position, meaning the valve does not need power to energize that port. Then the dash switch would trigger the valve and the gauge to activate the other tank. Hope that makes sense.

This is 100% correct.

Many old F250 drivers all learned this the hard way. If you are planning a long trip, you would want to start out on the Aux tank, and when the aux tank runs empty, you switch to the main tank. If you wire it correctly, (like what .94 OR says) then when you crank the engine, the solenoid valve drops out, and defaults to the main tank.

If you wire it backwards, then when you crank, the valve drops out, defaults to the Aux tank...and that's the tank you just emptied. So it never primes. It's very frustrating for your carb to be out of gas when you have a full tank.

Another reason for doing it is because the solenoid mechanism to activate the valve has a limited number of cycles before it wears out. If you power the valve in the "main" position, then every time you cycle the key, start the engine...the valve switches. So you want to reduce the number of cycles, and you do that by having the default (unpowered) position be "main."

You might remember this in the late 1980's passenger cars. When they first started doing automatic door locks. The solenoids for the door locks were not rated for infinite cycles. So every time you start the car, it locks the doors. Then you have to unlock. Start moving, and it locks again. The net result is a bunch of dead door lock solenoids on the back doors of a 4 door sedan. (because those solenoids were small and weak.) Even if no one ever rides in the back seat. The same thing happens on your fuel select valve. You just can't hear it cycling.

 

[Steve83]

Try this:

(click this text)