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Perfect! Thanks Ross.

Still playing with the mystery of the haunted fuel guage.

What is the normal ohm range of the 37 AC fuel sender?

Also, one other potential cause. The Runtz 12v to 6v module I am using is outputting 8v without the motor running. A quick search has people reporting that is a failed unit.

Could that be causing the issues I am seeing?

The 12 to 6 V unit might be a problem if it is not regulating as it should. The dash gauges are very sensitve and need a stable power supply. Many older cars have a small voltage regulator to stabilize the gauge circuit power supply. These often malfunction as they age and can cause poor and erratic gauge function or no function at all. I once had a '52 Cadillac convertible with 6 volt gauges and a 12 volt starter and generator. I put an old radio volume conrol in series with the power suppy to the temperature and fuel gauges and adjusted the "volume" until the gauges were fairly accurate and stable. That trick worked very well for years. I've had issues with late 1960s Ford pickup gauges that were caused by a malfunctioning gauge voltage regulator. On those vehicles, the regulator was a little metal box with two wires attached that was mounted on the back of the gauge cluster.

I checked the output with the car running and charging and with the motor off. It was a stable 7.99 or 8.01v. So the output is not jumping around. So I went back to the tank and disconnected the tank sender wire where it is spliced into into the harness going forward. The ohm reading between the wire and frame and the wire and bare metal on the tank is the same. So not a bad ground situation.

It's got to be the sender. The ohm reading I am getting is 390. Then I shook the car and waited for it to settle down. Then it read 460. Repeated the test again and then it was over 1000. Tried multiple run and after stabilizing, I got readings between 150 and 2200. So the sender is just being nuts. I would imag9e the sender range should be somewhere between 0 and 300. No wonder the guage keeps pegging to full.

What is the expected range on a 37 A/C sender?

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Drained 5 more gallons put of the tank. I would have expected the ohms to drop as the fuel level got lower. Nope, it went up. Now 1400ohms.

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I would say you have a bad wiper contact to the resistance wire. Perhaps along what was shown of the gunked up wiper Larry Reber posted in his photo.

Have no idea what the range should be or even the brand gauge your 37 used but doubt the max number will be much over 100 ohms until you get into postwar cars. Stewart-Warner magnetic gauges which Packard used with 41-47 Clippers used the old 100 to 0 S-W range and even the modern S-W range only goes to 240.

For what it's worth here are a few typical ranges. Except for the 48-50 Packard models the other years should all be straight resistance senders. If anyone knows the ranges for another year Packard I will be glad to add it to the chart.

EDIT: Updated chart with 37 sender resistance as was found by Kev.

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While we trying to see the mysteries of the fuel guage. Here is something else. What is this mount for? Snubber? Ground strap?

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Pivot for the e-brake mechanism----but I thought that bracket was on the pass side.

Parts list illustration on page 9 shows the equalizer pivot on the right side but it is actually on the left

Noted. From the angle I was looking at it, it didn't look like anything was connected. But yes that makes sense now.

I was looking for the hole in the frame the battery to frame ground strap mounts. But I didn't see anything obvious. Does it share a bolt with the battery box support frame?