Here is an indexing plate I made for installing the remote control unit in the dash. You can ignore the two large holes near the ends, as this was just a piece of material recycled from some prior life. The remote control unit is a rotary potentiometer. It is desirable to prevent the body of this device from rotating in the mounting panel (in this case the dash). Many such devices will have a flat side on the threaded mounting collar to prevent rotation, but that requires mounting in a "D" shape hole, which is inconvenient for the home installer without the proper metal punch. This particular pot has a full round threaded mounting collar, and you can drill a round hole in the panel. To prevent rotation in the panel the pot has a finger protruding forward near one edge of the front face. For normal production assemblies there would be a small hole punched in the panel at this location, and a metal faceplate might cover the small hole. In this case there is no faceplate on the front of the dash, and the control knob is small enough that it may not cover the small indexing hole.

So rather than drill the small hole in the dash I made this plate that has the small hole, and the plate will snuggle up near the top lip on the back of the dash to prevent rotation. The plate is 1/8 inch thick to match the length of the index finger on the pot. You could use a thinner plate if you were to file or grind a little off the length of the finger. The center hole is 5/16" diameter to accept the mounting collar on the pot. The smaller hole near the edge is 1/8" diameter to accept the index finger on the pot. The plate has to be wide enough to accommodate the two holes, and one edge of the plate has to extend beyond the side of the pot so the plate can come close to the (anti-rotation) flange on the dash. The length of the plate is not important, but in this case one end has to be short enough not to interfere with a nearby protrusion on the back of the dash where the wiper switch is mounted (which you will see on the next page).

Above you can see the pot mounted in the plate, viewed from the front, with the 5/16" threaded collar and the 1/4" shaft, but without the retaining washer and nut. The indexing pin is clearly visible in the small hole. Below you can see the same assembly from the back, ready for installation in the dash.