Bit of a silly question, but where should I be looking to see if my bike has had the splice done?? Airbox has no extra holes in it either, but after all these years I can't believe it's still standard, as it's a recent import. (unless their laws don't alow this)

The splice starts tight up to the ecu right at the back of the seat by the rear light. Depending on how well it was done it will be very obvious or very subtle

Tell us what model is your bike.

Sorry forgot MC21, tried to add it to my profile but can't seem to do it or find a 'box' to fill it in?

Did you find the wire splice ?
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MC21R ; MC21SP , plus some other none Honda 2t's

I have also MC21 you should looking for the PGM III unit.
You can find it at the end of the bike close to rear stop. The PGM III have 2 connectors one black and one white. You should be do a easy conductivity test between Orange/Blue wire at the black connector and the Black/White wire also at the black connector that goes into the unit. If your multimeter beeps your bike have the wire splice done correctly, but if not beeps there is no wire splice done to your bike.
Hope this helps.

Greetings George.