The HRC delimiters are different for each model.
The MC18 and MC21 delimiters are in the form of an in-line unit between the wiring harness and the PGM unit, the MC28 utilises an HRC "card" in place of the usual ignition card.
The MC21/28 HRC units will not simply fit a standard wiring harness. See the ignition page in the 250 tuning section to see how to modify the MC28 harness to accept the HRC card, and the MC21 harness to delimit the stock PGM unit.
To fit an HRC delimiter to an MC21 requires slightly more major surgery, but is basically a case of splicing in the wires colour-for-colour, in-line.
The MC18 delimiters plug directly into the stock harness.
Andy.
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