The 21-HW (female) is a circuit board with a 21-pin NEM660 (MTC21) socket and solder pads to connect wires. The female 21-pin socket may be used to adapt a harnessed decoder such as the WOW101 or T4 onto a 21-pin locomotive or motherboard. A pin-out of the 21 pins can be found Here.
To solder wires to the provided pads simply:
Each pad on the 21-HW is labeled. These pad labels are as follows (from left to right with pads facing you)
| Speaker (-) | Speaker(+) | Function 6 | Function 5 | Function 4 | Function 3 | Ground | CAM/Aux Input |
| Function 2 | Left Rail (Black) | Motor (-) (Grey) | Yellow (F0R) | White (F0F) | Blue (12V+) | Motor (+) (Orange) | Right Rail (Red) | Function 1 |
IMPORTANT NOTE (NEM660): The 21-HW adapter does not feature output transistors on Functions 3-6. This conforms with the connector standard. The logic boosters for these functions will be included on the Motherboard (if supported) unless otherwise specified by the manufacturer.