Commodore 64/128 Diagnostic Harness

$49.00$69.00 USD

This diagnostic harness will help make sure that your Commodore 64 or 128 is performing up to spec.


SKU: HARNESS Category:


Here’s what’s included in the kit:

  • User port loopback plug (in easy-to-insert angled case);
  • Cassette port loopback plug (in easy-to-insert angled case);
  • Joystick switching adapter (w/ case);
  • 3.5mm wind-up cable to go between cassette plug and joystick adapter;
  • Serial port loopback plug;
  • Keyboard loopback plug for C64;
  • Optional: Keyboard loopback plug for C128 & C128D (has switch for boot-up while inserted).
  • Optional: Cassxtender™ cassette port extender (required for fitting cassette plug into C128D).


  • No messy wires or multitudes of cables;
  • Fully supported by Commodore 586220/785260 diagnostic software;
  • Cases made of sturdy 3D-printed ABS.

Does not include BackBit cartridge which supports diagnostic software (available for purchase separately).

Additional information

Weight 6 oz
C128 Options

no 128 extras, w/ 128 dongle, w/ 128 dongle & Cassxtender™


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