Computer controlled OTA TV antenna.

Step 3 Which wires are which?

You need to find the common wire to know what to hook the +12 volts to. Normally the other wires are in order(like the last pic below) but not always.

Using a multimeter:

   1. Each of the two phases should have the same resistance when measured with a multimeter. When measuring the resistance across one wire from each of the two phases, the resistance should be infinite because the circuit is open. Locate the two pairs of wires that represent the two phases, and both pairs of wires will have similar internal resistance.
   2. Connect each phase to the amplifier and ignore the polarity (+ / -), for now. You have a 50% chance of guessing right.
   3. Send a command to move the motor. If the motor rotates in the wrong direction, then switch either phase A and A- or B and B- (effectively reversing directions).

Common will be half the resistance to any of the wires compared to the resistance of one phase.
I.e.
A+ to B+ = 144 ohms
A+ to B-  = 144ohms
B+ to A- = 144 ohms
B- to B- = 144 ohms
Common to any other wire is 72 ohms. Do not hook anything up till you are sure of this!! The last picture is an example that worked for me. It may not work for you.

Note: I am using I think a Teac 14769070-30 4x0 4 stepper motor,