5V conversion help needed

64_Barracuda said

Bill, where did you get the ohmic values from? Just curious I plan on building a gauge tester very soon.

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I'm not Bill but I have an answer... The pic is of the label on the tester that dealers service tech used. I don't think anyone knows who added those ohms values to the pic but they are pretty much correct. The senders have a 80->10 ohms range. 80 ohms should generate no needle movement, thus a invalid test. Approx' 74 ohms will move a needle up to the 1st hash mark in most examples.
Approx' 23 ohms is the center of the range.
10 ohms should get high end of range. In most examples that needle position, like the 80 ohm or home/off position, is set with physical stops.
Lesser ohms/resistance for extended period will overheat a gauge.