Hi There
Good choice MC 21 good road and great track bike, The 3 wires you are talking about the middle one is live, you only have to join the 2 outer wires to override the side stand operation issue,
Get some pictures up of the bike, what else does it need before you can ride it ?
all the best,
PS I have got the metal surround for the toolbox inside seat unit
jonmac
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John