Fuel Gauges, Senders and Tanks

Usually when both gauges die at the same time, the common culprit is the negative leads to the meters or the tank senders.
What work was done anywhere just before your failure?

Testing;
With the gauges and on, what voltages do you see on the 3 back wires? Not the back light wires.
You should have B+, B- and signal.
Measure these B+ & B- to other good positive and negative leads. If your volt meter works, use these leads.
Then measure the resistance of the signal wire to a known good negative source. Between 40 to 400 ohms (pending tank level).

Let us know what you find

You may have knocked a ground or B- lead loose.
I'm not allowed past the Carolina's anymore so I'm not available to come to assist.
Retrace your path looking for any wire crimp that may have been knocked or wiggled loose.
Even a water hose blast may have induced a bad connection.

Tank grounding is often used for the battery negative lead.

This is important as tank grounding is also an anti-static issue.
Static makes fuel go BOOM.

My first obvious step is to swap gauges and see if the problem follows the gauge. My second obvious step is to run a temporary wire from the gauge to the senders after confirming the voltage to each gauge.

To be clear, you swapped sender feeds, and now both gauges read "accurately"? If so, when you swap them back does the problem resume, or?

Both gauges work properly if they are swapped, but only one works of put into proper orientation? I'm not seeing the ground as the issue, but wondering about the relationship of the blade connectors to the individual gauges. Inspect the blades on the gauges as well a the wire side crimps. Consider replacing both crimps to fresh wire.

Until you can get to the second sender, sounds like reversing the gauges gives you a temp outcome. Next step would be a temp wire from gauge to sender on the first sender you can access. Run over the floor for a quick test.

Make one meter read accurately. Prior to you reversing them it seems to have appeared one was working. Now neither work which suggests that one was reading improperly.

yes, seems like a ground is being introduced by one of the wires.

I'm having some trouble following you here. Posts #7 and #9 both read that you were able to make each gauge and sender work when reversing the sender leads. Is that not the case? Have you measured ohms on both sender wires while disconnected from the gauges??

Get a meter on the sender wires and measure the ohms.

If they read fine in one arrangement it suggests the wires are ok. Need meter to show the issue.

[QUOTE="92Searay-37', post: 365580, member: 35015
When sender wires pulled off one gauge goes to full, one goes to empty.

When I ground the sender post the full gauge went empty, the empty one went full.

[/QUOTE]
Sounds like the gauges are different brands.

Sounds like the gauges are different brands.[/QUOTE]

By the looks of the photo they are different brands. He needs to check ohms with a voltmeter to sort out condition of the senders and wires.