I have put in a dash and the gauges form a 1940 standard in my 1940 ford truck. The truck has been updated to a 12 volt system. The fuel oil and temp gauges have a 12 volt to 6volt reducer. My question is how have I get my volt gauge to read correctly? Thanks Sent from my iPhone using The H.A.M.B. mobile app
It shouldn't be a voltmeter, should be an ammeter. The short answer is you can't get it to read 'right' if your charging system output is higher than what the gauge reads. If you stuck with a generator, it should work. Alternator, it will work but won't be able to read full output and that may take the gauge out. I believe the OEM gauge is a 'inductive' type (no direct wire connection, just a 'loop' the wire goes through). If you've changed the ammeter to a voltmeter, simply hook the positive terminal to a switched 12V source and ground the other side.
i've done 12 volt conversions several times on `40 Ford gauges. i used those Runtz voltage drops on the fuel/oil/temp gauges. i believe they regulate the voltage to 6 volts, which wouldn't work out with the volt gauge somewhere here along time ago i asked the same question , someone told me to put a 60 ohms resistor in the power feed to the gauge...works great! when you switch on the ignition the needle will go into the yellow , start the engine and the alternator puts the needle just into the green pictures stolen from Bills1940
Use a 60 ohm resister on the original voltmeter. I asked the same question years ago and was advised to use the 60 ohm resister. Works good in my 40
With the knowledge supplied by "Flat Ernie" on Fordbarn I converted my 1940 Ford DeLuxe BATT gauge to operate on 12V by isolating it from the rest of the gauges and doing what's shown with a 60 OHM resistor in posting #6 in the thread below. No runtz gizmos. Has been working fine last 10 years. Hope this helps. https://www.fordbarn.com/forum/showthread.php?t=48622&highlight=convert+voltage+guage+12v
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