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6 volt gauge power...why?

6 and sometimes 5 volt were common on early gauge sets. One theory I heard was to limit the fault current in case a sender shorted out. Most gauge senders go to ground so if it shorted out completely limiting the input to the gauge to 6(5) volts would protect the gauge. I used to have an IH mini dumptruck that had 5 volt mechanical regulators. I wound up replacing with a solid state one I built.
 
6 and sometimes 5 volt were common on early gauge sets. One theory I heard was to limit the fault current in case a sender shorted out. Most gauge senders go to ground so if it shorted out completely limiting the input to the gauge to 6(5) volts would protect the gauge. I used to have an IH mini dumptruck that had 5 volt mechanical regulators. I wound up replacing with a solid state one I built.
Well that makes some kind of sense I guess. Just makes things challenging if a person wants to keep originality. I have taken apart both the gauge and sender (MacGyver is my middle name). Gauge is fine, sender appears fine but not moving full range on the resistor windings, can't get anything less than 25 ohms at 40 psi test air pressure...and I need 10 ohms in order for the gauge to read 40 psi (have tested with a standalone resistor). Tells me the rubber diaphragm has stiffened up over the years and won't move far enough. Some things are just beyond refurbishing...which I hate to admit!
 
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