Welcome!
As it happens, timing is perfect! It just so happens the just released issue of the Heart of the Beast contains an article by Marc Haibeck that focuses exactly on "NO START" issues. If you join the ZR-1 NetRegistry as a member, you'll have access to all the magazines, and a wealth of information.
However, here's a "teaser" from Marc Haibeck's super article (schematic can be found in the FSM, sans the arrows and voltages that Marc included).
I gather by your post that you know your way around a schematic and a VOM, so this should help a great deal. "Poke" around and let us know what you find. But, let me ask this, since you bypassed the clutch switch already, probe the big purple wire routed under the rear of the plenum and let us know if you have 12 volts when the starter switch is engaged? And, if so, do you hear a "click" from the starter solenoid when you turn the key? If yes to both, then the main contact posts and "ring" in the starter may need some attention. But, rather than jump around, it is probably best to let you look at the schematic and then we can break it down methodically further, if need be.
Good luck, and again, welcome to the
BROTHERHOOD OF THE BEAST!