# How to identify a potentiometer?

I am trying to find the specs for a potentiometer that isn’t marked. I want to find a pot that matches the specs for the one I have. I want to add a second pot to the circuit so I can control it from two locations. I have identified the wires and voltages but am unsure of how to check resistance of the pot. Wire diagram RED 5 volt supply, BROWN ground, WHITE signal.

Hello @socokid - If you are able to remove the potentiometer from your circuit, you can use a multimeter to measure the total resistance of the pot. Set the multimeter to ohms and place the red lead on the red wire and the black lead to the brown wire. If your meter is not autoranging, you may need to try multiple resistance ranges to find the correct value.

After measuring total resistance turn the pot to midrange and measure the resistance between the wiper and an end. If it’s about 50% of the total resistance it’s a linear pot, if it’s about 10% or 90% of the total resistance it’s a logarithmic pot.

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I put an ohm meter on it today.
Red to Brown 2973 ohm
Red to White 175 ohm
Brown to White 3102 ohm
This was with the pot disconnected from the circuit. The strange thing is there is no change in resistance with the position of the switch. With the circuit powered I have:
Red 5 volt
Brown ground
White will range 0.425 volt to 4.560 volt depending on switch position.
This circuit controls the engine speed in a tractor. I want to add another control outside of the cab so I don’t have to enter the cab to control it.

It looks like it would be a 3k ohm potentiometer. The resistance value will only change if you are testing between the wiper and one of the outside terminals. Since it is for speed control, it is mostly likely a linear taper, but you can confirm by testing the resistance at 50% like the previous post indicated. If it is roughly 1500 ohms at 50%, then it would be linear. We don’t carry anything in stock at 3k ohms. Closest option is this one at 3.5k - 480-5942-ND

Given the voltage levels you measured it is possible that adding wires more than a few inches longer than the original to the pot may cause unreliable circuit operation due to noise pickup. It may work fine for days or weeks and then suddenly slam the value to one end of the range due to specific noise patterns. So be very careful as you don’t want uncontrollable acceleration in a vehicle.

This method is pretty good, thanks bro.