Whirlwind MCT-7 Cable Tester

The MCT-7 is the diagnostic tester rather than the pass/fail one. Its rotary switch steps through each conductor in the cable in turn, so instead of a red light you get to see exactly which pin goes where, which is how you identify an unmarked or non-standard lead.

It has connectors for NL4, 5-pin DIN, BNC, XLR, TRS, RCA and 3.5 mm, which covers most of what turns up in a road case in one box.