What you have described is a resistor, not a voltage regulator. It reduces voltage, but it does not regulate the output voltage. The voltage at the output will vary with the current drawn by the load. Think of it as a ballast resistor for an ignition coil - like the one that we saw mounted on the firewall of a lot of cars way back when.
An electronic unit is a very good choice if you are working with a 12-volt to 6-volt conversion, but in the case of a 6-volt system you only want to drop a couple of volts and most of the readily available voltage regulators need a higher input voltage that the normal 7.4 - 7.5 volts you see in a 6-volt system at normal charge levels.
If you are dealing with a 12-volt system, this would be a good choice:
But, if you are still 6-volts, I poked around a bit and I found a couple of units that will probably do what you need at a cost that won’t break the bank.
This one is the original relay style. While it is an Old School approach, it will work just like the defective one you have. This one appears to have an adjustment screw to fine tune the output voltage if you need it.
REGULATOR, Instrument Voltage, electronic replacement, no adjustments necessary, more reliable than the original relay style regulator, output is a constant 5 volts as required.
1948-1952 F1-F3 AS VOLTAGE INVERTER
For both units, the IGN terminal is the straight tab and the “curled” tab goes to the gauges. Get it backwards and it won’t work. And, the tab is an electrical connection - screw it down to a good ground point.
Found this new-to-me windshield. The old on was missing glass and the whole bottom was rusted out. Had about 1/4 " of putty. This one is the newer 69-75 style with the wipers mounted on the bottom to have taller glass. I have the wipers wired and working. It even has somebodys graduation cap tassle from 1974. Which if it's from high school they would have been born in 56 the same year as my jeep. I also tried wiring the gas guage. At empty the guage reads 1/2 and at full pegs the guage past full. I thought it was becuase the guage is 6 volt and I have 12 volt going to it. so I got a 12-6 volt reducer and it's still reading the same. I checked with a voltmeter and still have 11.5 volts at the guage and 12.5 on the battery. I don't know if the reducer is bad or what it is. Whould like to hear your thoughts.
This probably has more than you really want to know about instrument cluster regulators.
I drew a quick diagram of how the regulator sits in the circuit. If you have 11.5 volts out of the regulator, it is fried. You should have about 5-volts out of the regulator. If it is working properly, it will drive a digital meter nuts and it may make the needle on a good old analog meter quiver around. Either the contact points are welded shut or the heater for the bi-metal strip has opened. You have nothing to lose – pry it open and see what you can find.
As I said in the last discussion, just about every manufacturer used the same type of regulator. If you can find one for a ’56 Ford, Chrysler, Dodge, Chevy or whatever – it will be very close to the one you have.