[hatzie]

Each fuel pump gets power from the polarity reversing switch and ground from the frame.

The fuel gauge sender select switch is in the valve. There's no reason the gauge switch couldn't fail in one position or the other and the valve itself still route fuel correctly.

Try this;

• Get some 1/2W resistors in 100Ω, 47Ω, and 22Ω. or close to those values.
• Get some alligator clip electronics test leads.
• Get a handful of MALE Weatherpak terminals. Wire gauge rating is not important... you're using these to make sure you don't damage the FEMALE valve plug terminals by jamming stuff in them that isn't supposed to go there.

I keep male and female Weatherpak and Metripak 150, 280, 480, & 630 terminals in my meter bag along with several other connector families so I can do test hookups without damaging sensors and wiring harnesses. U-Line sells small plastic Ziploc baggies. They're darn handy to keep these kinda test terminals separate in the meter bag. I use blue tape and a sharpie to label the oddball terminals.

1. Unplug the six position Weatherpak tower plug from the valve.
2. The fuel gauge should go to the 3:00 position with the ignition on.
3. Attach the jumpers from a known good ground and a MALE Weatherpak terminal in the B terminal of the valve plug.
4. One at a time insert the 100Ω, 47Ω, and 22Ω resistors in between two jumper leads and look at the gauge with each resistor.

   100Ω should drive the needle to just past F, 47 should drive it to somewhere around 1/2 and 22 should drive the needle below the 1/4 mark nearer 1/8.

5. Insert two Male Weatherpak terminals with two test leads jumpering from B to A and watch the gauge with the ignition switched on. This is one of the actual senders.
6. Insert two Male Weatherpak terminals with two test leads jumpering from B to C and watch the gauge with the ignition switched on. This is the other sender.

If the senders are both working and the tanks are at different fill levels the gauge should read different levels in 5 & 6.
If your tanks are filled to the same level then the gauge will read the same in 5 & 6.

Steps 1-4 are a sanity check to make sure the fuel gauge and the associated wiring is in proper calibration. This is a bitmap of a curve I plotted in Excel based on squarebody fuel gauge needle position vs a calibrated decade resistance box in place of a GM sender on my bench.