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Thread: Is my ‘56 truck 6V or 12V

  1. #1
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    Is my ‘56 truck 6V or 12V

    As mentioned before, my new, to me, ‘56 truck has both 6V and 12V bulbs.
    Already started conversion to 12V. Alternator, coil, condenser etc.
    Headlights are 6V. Dash bulbs are 14.4V.
    There has been talk of a 12V to 6V resistor.

    My concern is avoiding damage to any of the gauges by running 12V to all.
    Are resistors needed and which ones need to be protected.

    Here are some pics. What’s the small rectangular device above the fuel gauge. Resistor?866D0195-6A71-47D6-AEBF-CD32779211D7.jpg
    Last edited by M37grunt; 11-22-2019 at 09:18 AM. Reason: duplicate pic

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    Super Moderator LarrBeard's Avatar
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    It looks like a bunch of posts have disappeared. That happens, rarely. When I get back to the computer at home I'll start over.

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    Thanks Larry. Take a look at the pic I sent. Tell me what that small rectangular thing is on top of the fuel gauge.
    JB

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    Super Moderator bmorgil's Avatar
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    Quote Originally Posted by LarrBeard View Post
    It looks like a bunch of posts have disappeared. That happens, rarely. When I get back to the computer at home I'll start over.
    My fault all. Accidentally deleted the whole thread! Thanks for the re post M37grunt.

    I think Larry you clarified:

    The gauges are 6 volt run off of a mechanical voltage reducer.
    The bulbs are 12 volt.
    the 6 volt headlamps and gauge lights don't belong.

    The wiring diagram. https://www.kaiserwillys.com/tech-gu...26-4x4-and-4x2

    I think that "rectangle device" is the reducer. You had 2 photos from the back side. Can you re post those? We will see what Larry thinks.
    Last edited by bmorgil; 11-22-2019 at 05:06 PM.

  5. #5
    Super Moderator LarrBeard's Avatar
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    Six Volt or Twelve Volt; Probably More Than You Wanted to Know

    OK – let’s try to figure this out …

    You have a 1956 Jeep Truck with an L 226 engine. By the best Jeep sources, a 1956 truck was originally a 6-volt truck – the change to 12-volts was in 1957. It would have been a generator system, not an alternator. But – a model year 1957 could have been bought in 1956 and Jeeps are notorious for being misidentified as to year.

    It really doesn’t matter much since the 12-volt conversion is well under way. The First Rule of Jeep is that “What You See is What You Have”. Don’t spend too much time trying to figure out “Why” – Jeeps are also notorious for half-finished projects.

    You have mentioned 14.4 volt bulbs several times. We speak of 6 and 12-volt systems, but a “6-volt” system runs at about 7.2 volts with the motor above idle and a properly operating generator and voltage regulator. Guess what? A properly operating “12-volt” system runs at twice that – the 14.4-volt rating on the bulb! One mystery solved.

    Now, let’s get back to the vehicle in question. The instrument cluster picture shows a module above the gauge assembly. This is indeed a voltage reducer. (That’s why I suspect that the truck is a 1957 or later). When most vehicle manufacturers (Ford, GM, Studebaker, etc.) went to 12-volt systems, they did not switch instrument voltages – they just added a “voltage reducer” to the instrument cluster. Now, if you are just working with a single gauge, with a constant or nearly constant electrical load, a simple resistor can do an “OK” job in reducing voltage. But, when you have several gauges the load varies and you have to do something different. You don’t want oil pressure to change when you fill the gas tank!

    The answer to the problem was a mechanical voltage reducer. It operates a lot like an old-fashioned “click-click” turn signal blinker. Half of the time it puts 14.4 volts on the gauges and half the time it puts zero volts on the gauges. That’s an average of 7.2 volts, which is just fine for the slow responding King-Seeley gauges.

    Now, being curious folks, we want to know just how does this voltage reducer thingy work (technical term there). Now – up front – I’ve never torn one apart to look it over, so details may vary. There were two versions of reducer and I can’t tell just which one this is just by looking. Look at my first picture, Ver 1. It is a three terminal device; input from the ignition switch, output to the gauges and frame ground through its mounting screws and the gauge cluster. It needs a good ground to work.

    It has a bi-metal strip in it (think thermostat) that makes up two sets of contact points – one normally open and one normally closed. There is a heater wrapped around the strip (or the strip itself may be the heater) but to explain it a separate heater is easier. When you turn on the ignition, the switch connected to the heater is closed and the heater .. heats up. As it heats up, it causes the bi-metal strip to bend. After a bit, the switch to the gauge closes, putting power on the gauges. But – at the same time the switch to the heater opens and the heater cools off. As the bi-metal strip cools, it opens the gauge contacts, closes the heater contacts and the process repeats; “Click – click”. You probably won’t hear it because the strip is so small and it moves only a few thousandths between open and closed.

    The other version, Ver 2., uses just the current drawn by the instruments to heat the bi-metal strip with no separate heater. It is simpler to manufacture (cheaper), but the ON-OFF time of the “Click-Click” will vary as the various sensors change, but this may be considered as “good enough” for the day.

    How does this connect up to the cluster? The second picture is what I’ve dug out of the wiring diagram. The Instrument lights are fed from the Main Light Switch, which I believe has the dimmer built into it. These bulbs operate from the full battery voltage through the panel light dimmer (our 14.4 volts), so they are properly 14.4 volt bulbs for your “12-volt” conversion.

    As you can see, each gauge has its own variable resistor as a sensor. As these sensors change (oil pressure, gas tank level, engine temperature), the current provided by the voltage reducer changes. If the reducer was just a resistor, the voltage applied to the gauges would change – not a good thing even with 1957 technology.
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