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'55 Instrument Voltage Regulators

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  • '55 Instrument Voltage Regulators

    This morning, I received this email from Stan Reynolds in Grass Lake, Michigan regarding a problem he is having with his fuel gauge readings. He is a member of Yahoo Classicbirds and someone there recommended that he contact me for help with this problem. I have invited Stan to join us so that he can communicate back and forth with ya'll on this. Here is the problem he has with his '55 Tbird which has gone through a partial 6V to 12V modification prior to him buying it.

    "Hello Ray,
    My name is Stan Reynolds, and I live in Michigan. Your name and email address popped up during a discussion on the Yahoo Classicbirds mail list regarding instrument voltage regulators. The person who recommended you said you are somewhat an expert on such matters, so I'm hoping you can also give me some advice with a problem I have.

    I have a 1955 Thunderbird which has been (before my ownership) given a partial twelve volt conversion. The starter and window motors are still six volt and, although they spin at twice the speed intended, they still work and have done so for the twelve years I have owned the car. My problem is the fuel gauge has never registered over one quarter tank even when I know it to be full right up to the fill pipe. Several years ago, I replaced the sending unit in the tank with a new 12volt unit, but the result was the same. It's as if the full scale of the gauge has been compressed to the first 1/4 reading.

    A few years ago, CASCO (a company in Ohio that sells classic bird parts) developed a "matched set" for cars like mine that includes a sending unit and a gauge that is matched to it. I suspect this may solve the problem, but have been reluctant to order it because it is very expensive and also requires removal of the instrument cluster, a job I swore I would never try again. I removed it once to replace lightbulbs, and spent the better part of a day trying to wrestle it back in place without unplugging anything.

    In July of this year, a guy wrote to the mail list that he had the same exact problem with his '55 and that he had taken it to a place called Quality Coaches in Minneapolis. They had installed a "resistor", not sure where, and it solved his problem and the fuel gauge now works normally. I contacted this guy, and he gave me the name and phone number of the person he had worked with at Quality Coaches, but when I contacted them they acted as though they had no idea what I was talking about.

    So, after a long-winded introduction of the issue, I am hoping you might have an idea what the other '55 owner was referring to. I am also hoping that if you know of such a resistor or other device, that it could be installed in the trunk on the feed line from the sending unit.

    Thank you, and I apologize for such a long message.
    Stan Reynolds
    Grass Lake, Michigan
    55 red and 57 white E"

    I have replied to him already and given him some information regarding how the factory handled the step down of the 12V from our system to 6V for the gauges. I sent him the link that Alexander created many years ago on how to fix this problem and adjust the readouts on our Squarebirds. It may be that this is the route that he might have to go to also, as someone apparently did. But when he talked with that coach company, no one seemed to know what he was talking about. Can ya'll help? I asked him to watch this Forum for responses.

    Ray Clark - Squarebirds Administrator
    '59 Tbird "The Yellow Rose Of Texas" aka "Tweety Bird"
    "It's Hip To Be Square"
    Thunderbird Registry #33025 VTCI #11178

    Contact me via Private Message for my email address, or (Cell) 210-875-1411 (Home) 210-674-5781

  • #2
    The Thunderbird line came at a unique time in the evolution of Ford cars.

    1955 T-birds were fitted with six volts and positive ground. (all gauges and devices were six volts, and had been for many prior years).

    1956 T-birds changed to 12-volts and negative ground, BUT all the gauges were also changed to 12-volts. The same happened across all lines of Ford cars and trucks. This is the ONLY year Ford used 12-volt gauges.

    1957 T-birds retained 12-volt/neg gnd BUT the gauges went back to six volts. Again, this happened across all car and truck lines.

    For some devices, this swap is easy. Not so for everything. Stepping down voltage for gauges can be done with a good constant voltage regulator under the dash. If a 12-volt generator is used with a 12-volt battery, the charging system's voltage regulator must be swapped as well.

    The only difference in the starter motor and generator is the field windings. As stated, the starter motor simply runs faster which tends to make the engine start sooner. A shorter duty cycle keeps heat down, so no change is necessary. The clock is a solenoid-operated device that needs no alteration.

    Permanent magnet motors will run backwards and a lot faster. Since we have used resistors for speed control successfully, the heater motor leads need to be reversed with the addition of a modern heater motor resistor for speed control.

    Change all bulbs to 12-volt including the dash (especially the GEN light) and radio lights, dome, glove box, stop, signal, running, backup, headlights, etc.

    The radio needs to be retrofit to 12-volts OR all the tubes must be changed to their 12-volt counterparts and the '55 radio vibrator needs to be changed. Gary Tayman Electrical does a beautiful job of retrofitting these radios, giving them AM FM AUX stereo with left-right and front-back fade. He did two radios for me and I'm happy because the radios look BONE STOCK. His number in Sarasota, FL is (914) 317-8924. Gary is also a T-bird owner.

    Each gauge has two posts. I would add a constant voltage regulator and reverse the polarity of both gauges. When done this way, the original sending unit may be retained.

    It's easy to understand the need to standardize across car accessory lines but Ford made major electrical changes in '55 thru '57. The next change came with fitting alternators because of higher current demand. It continues today with electric fans and electric water pumps that run when only necessary for more efficient and gas-saving heat/cool control.
    - Dave
    My latest project:
    CLICK HERE to see my custom hydraulic roller 390 FE build.

    "We've got to pause and ask ourselves: How much clean air do we need?"
    --Lee Iacocca

    From: Royal Oak, Michigan


    • #3
      12V 56 Thunderbird guages and all other electrical parts will swap into a 55 that has been converted to 12V. There are some minor wiring differences in the 2 years, but this is a very easy swap since 12V parts are available. Resistors will also work, but all the components are avail as a direct fit.