Put down the knife and fork
that's what the colors are, I'm just trying to figure out how to bring the Arduino into it, whether I need to do something with the red+ coming out of the gauge, or ignore it since I'm powering the white directly. Last night, I powered up the gauge, wired the black and white wires to the arduino and punched in a frequency. The odometer started rolling, so I know it was working, looks like the next step is to figure out the frequency/speed correlation. For some reason, the speedo hits 20 when I power it up (it is possible the needle isn't zeroed) but I can only get it to respond to a certain range 15-30mph, regardless of the frequency.
I think I'm going to rewrite it to sweep from 0Hz up through nHz and see if the needle sweeps, I've just been using a fixed value till now.