MrD did not really describe what trouble he is seeing.
MrD did not show us the gauge connections.
I suspect that the gauge is still connected to the key switch and accessory lighting.
I am assuming we are talking about an analog gauge.
Often OEM analog fuel gauges are wired with the purple wire to the Ignition switch Accessory power. (the key turns it ON)
In that case the gauge is always powered when the key is on and is not powered with the key off. The gauge was usually lit also, either with all the other gauges or by use of a jumper on the gauge.
Some single tank setups used a momentary switch to view the gauge. That way it was not drawing power all day.
(I hated that setup because you had to hold the switch to see the level while you were pumping gas...)
Dual tank setups used a switch to choose which tank was reading.
The best setup is to disconnect power from the Ignition switch entirely, including the gauge light. The OPs diagram looks right so long as that was done.( disconnect the purple wire)
Pins 4,5,6 are choosing the tank to read.
The jumper across 1 & 3 will provide power to the gauge when either tank is chosen but not when the switch is off. You must not still have power coming from the key switch or it will power the gauge regardless of your switch.
A quirk to this setup is that both switch lights will light in either of the ON positions(because of the jumper)
This setup allows you to turn OFF the gauge. Thats good.
I would light the gauge with the Gauge + jumpered to the gauge light power.
Thank you all for your help. I believe I can now figure this out. I am going to use Pins 1,2,3 to run power up to the gauge, and pins 4,5,6 for the tank sending wires and 1 wire to sending input of gauge.
Yes, gauge is analog.
Trouble was I did not try this configuration thus was not getting a signal sent to the gauge.
As Hookup1 says "Your diagram pins 4, 5 and 6 are all you need to switch the sending units to the fuel gauge. Verify that 5 pink wire does go to the fuel gauge." I now understand that the toggle switch really doesn't even need power, I am using the 2nd pole pins 4,5,6 to switch between Aux fuel tank and main fuel tank. This is what I was confused about. Pole 1, pins 1,2,3 will run power to the gauge.
I will be working on the boat later tonight and will report back.