The electronics on each model varies greatly, so Tom's problem could possibly only be applicable to 1989 models onwards. There is no wire splice for the 1987 MC16 and 1988 MC18 R2J/R4J-SP models.
If the bike has run fine once, and you have modified nothing, then it is highly likely a loose/bad electrical connection somewhere. Time to go through the whole wiring harness and check/clean each fitting.
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Andy.
NSR-WORLD.COM
Please keep all responses to Forum posts on the Forum so that others may benefit.
Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
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