Q: I opened one of my MIDI cables to fix a broken wire, and noticed that not all the pins are connected. What gives?

A: MIDI uses a 5-pin DIN connector; but only pins 2, 4, and 5 are connected – and, in fact, pin 2 (shield) is only connected on one end. This is done to create a telescoping shield, which helps prevent ground loops. Pins 1 and 3 (the outside pins) don’t have to be connected, though some cables come with them wired.

In the past, some manufacturers have used those extra two MIDI cable pins for non-MIDI-spec-compliant purposes, such as for MIDI thru or to carry “phantom” power for other devices.