1955 fuel gauge sender

[dmsfrr]

Originally Posted by Daves55Sedan

Yes! But my understanding (correct me if I am wrong) of the little constant voltage regulator is that it just has a set of contacts that flutter when voltage is applied and that it is not really a 6-volt resistor, rather a "buffer". If that's true, isn't his 6-volt guage overloaded?

I believe your understanding of the dash gauge regulator is correct, it 'flutters'. It's a high speed electronic switch that opens at a pre-determined limit then continues to open & close to maintain that limit.

Here's why I think the gauge seems to work correctly but takes too long to reach it's level after turning the key on.
The fuel sender in the tank works about the same way as the little dash gauge regulator, it flutters, but slower, to control the electricity thru the fuel gauge.
The fuel gauge needle is linked to a heated strip of metal... (refer back to the paragraph directly under the diagram in Beav's comment #4)
and the 'flutter' rate of the temp sensitive contacts in the sender self-limits the electricity passing thru the gauge. It's also why they should be a matching model year *pair*, the oem '55, '56 & '57 gauges & senders are made to different electrical specs.

I suspect having the dash gauge regulator also in the circuit is reducing the voltage/current a bit too much to allow the fuel gauge to 'warm up' to it's eventual reading in a normal amount of time.

Originally Posted by Daves55Sedan

I don't know how they originally obtained ground at the gas tank, since it was originally isolated from the body by rubber pads between the trunk floor and top of the gas tank. And the gas tank straps also have rubber pads, so they insulate the tank from ground.

I ran an extra ground wire from the firewall grounding screw all the way back to the gas tank sending unit and put a ring tongue terminal on it and bolted it directly down to one of the sending unit mounting screws. I tapped that ground wire at the first taillight and connected another wire to ground the tail lamp and backup lamp sockets so that I would never have ground issues with the lights back there also.

The original fuel tank ground? I don't know either. When I replaced my 55's tank there was nothing to see of how it was grounded except for the worn out & missing cushion strips.
Maybe it was thru the steel fuel line from the tank to the frame, but that seems like a suspiciously bad idea to me.
Installing an actual ground wire from the sender flange to the car body is a much better solution, and is on my to-do list. A previous owner spliced a rubber hose into the steel line out of the tank.

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[Daves55Sedan]

Originally Posted by dmsfrr

I suspect having the dash gauge regulator also in the circuit is reducing the voltage/current a bit too much to allow the fuel gauge to 'warm up' in a normal amount of time.

By golly, I think you're on to something here. But if he disconnects the constant voltage regulator from the fuel guage and runs a separate wire from the coil terminal of the start switch to feed the guage it means there will be 12 volts connected to a 6 volt guage. Won't it read double the actual amount of fuel?

Originally Posted by dmsfrr

Maybe it was thru the steel fuel line from the tank to the frame, but that seems like a suspiciously bad idea to me.

I think you've hit the nail on the head! It must be grounded via the fuel line connected to the car frame by those little push-in clips. I pondered like you wouldn't believe how it worked, but never thought of the fuel line!