[nuttle]

In addition, unless you place a jumper to get 6V on the power wire (when using a servo, for example), the power wire is not connected at the DSC. Spikes and (I suspect) all motor controllers use an opto-isolator, so by design there is no common ground. You have to use ground and signal but there is no need for the power wire. Note that for a Spike, there is actually one ground and two signal wires and the signals are on/off only (there is no Pulse-Width Modulation happening and this is why there are separate places for Spikes and motor controllers/servos to plug into the DSC), even though you see this called a PWM cable. When wiring a Spike for the compressor, my personal opinion is it is good practice to only connect the signal for the forward direction, so there is no way to run the compressor in reverse (which is very bad for most compressors). When we've made and used custom cables, we always only included the required number of wires and never had this come up in an inspection, FWIW.