RepRap for Science—How to Use, Design, and Troubleshoot the Self-Replicating 3-D Printer - Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs - page 147

FIGURE 5.50 Paired wires being tested with a multimeter.
The rest of the wiring is not terminal-specific, so you do not need to worry about polarity.
Once everything is wired up, check motor rotation with the interface described below and if it
is wrong, swap conductor pairs.
5.2.10 Limit switches
The next step is to gather the BOM of your limit switches as shown in Figure 5.51 , which con-
sists of the following:
Three mechanical limit switches and wires, three end stop holders (printed), three
M3 × 20 mm screws and three M3 washers.
Three M3 nuts.
Six M2 × 10 mm screws and six M2 nuts.
Three M2.2 washers.