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Forgot to mention...the 75s changed the wire colors both from the start switch AND the clutch switch. IF the wiring harness is for a "later" bike, and being used on an "early" bike, the colors will lead you to make wrong connections.
Once again...Why'd they DO that??
RickR90s...HOW did you specify the wiring harness that you bought?
Did the vendor make a selection available in the harness' available for the R90s, or just offer ONE choice?
AND...have you or anyone you know about changed the neutral switch? In neutral is it "open" or "closed".

Jean wrote:Forgot to mention...the 75s changed the wire colors both from the start switch AND the clutch switch. IF the wiring harness is for a "later" bike, and being used on an "early" bike, the colors will lead you to make wrong connections.
Once again...Why'd they DO that??

I think this is when the DIN standards changed as they adjusted to all the new features vehicles had developed which were not represented in the standards, so lots of manufacturers made some changes at this time to adjust to the new standards.

From my schematics this could be the problem.
In both years, the clutch lever must be pulled in (to actuate the switch) to permit the starter relay to operate. The wire colors changed tho, so if you had the older wires and hooked-up a harness with the new colors by just matching the colors, you could run into some INTERESTING action.
That's the reason for my questions about harness design...to Rick.

Hellllloooooooooooo Rick.
How's it going?