How would I avoid reversing the polarity?
The polarity does not matter. Hence do not worry about it.
However, if you are a perfectionist --
- Connect the positive terminal of your DVM to a good earth.
- With a probe connected to the negative terminal of your DVM, test the wires in the pair.
- The wire with the larger voltage reading is the B-wire and the wire with the smaller voltage reading is the A-wire.
- The B-wire should always "appear" on terminal 2 and the A-wire should always "appear" on terminal 5.
