trying to wire a DPDT 12v relay in truck

[Beefcake35]

HI,
Hoping someone can help me here as I am a novice. This is on a vehicle so I hope thats ok but I think it pertains. Long story is I have a old truck that has a valve that went bad and I cant get them anymore. It has a switch on the dash that has a single wire back to the valve that only has power in 1 position. The new valve is motorized that runs in different directions so it needs 2 different power sources. I have a DPDT relay I was hoping I could make work if I ran another power and ground (only when ignition is on). So what I thought was if I connected the existing wire (only has power when fuel selector switch is on) to the relay coil. Could I somehow connect the new power and ground to the relay and then connect the relay to the valve so I can still control what the valve does by the fuel selector switch? I know I could put in a DPDT switch but then it wouldnt control my gas gauge when I switch between tanks.

So today I have a fuel tank selector dash switch with 1 wire that goes to the valve. That also controls the gas gauge. The new valve has a motor and 2 wires and it runs in the direction depending on the polarity. I will run new pos and neg only powered when ignition switch is on to the relay. I just dont know what to connect where. I was thinking the existing wire from fuel tank selector switch to Coil... that would give power to NO. If I ran the new pos and neg to COM that would give power to NC. Thoughts? Any help greatly appreciated!!

 

[Lucien Nunes]

The first thing to be sure of, is that the valve can be continuously powered and not just given a pulse of one polarity or the other to change its position. If it can be left powered all the time the ignition is on, then yes it is simple to use a DPDT relay for this. Wire the coil to your existing switch and chassis ground. Connect the two common contacts to the two valve wires. Wire the N/O of pole A and N/C of pole B to chassis ground. Wire N/C of pole A and N/O of pole B to the ignition hot. I.e. the N/O and N/C of the two poles are cross-connected so that which of the two valve wires is positive and which is negative reverse when the relay changes over. I would sketch it but I am not near a suitable machine!