We're on a road trip on a 1973 R75/5 LWB and we rode in heavy rain yesterday. After I turned off the bike it wouldn't start again. Nothing happens when I push the starter but I can kick start the bike. I let it dry over night and same issue. There's no sound at all (no solenoid clicking) and the lights don't dim. Measuring the battery while pressing the starter shows no dip in voltage.

Jumping the black wire on the starter relay to the battery positive cranks the starter so I know the solenoid and starter works. Duane Ausherman has a great post for identifying starter problems (https://w6rec.com/electric-starter-troubleshooting) but my bike isn't wired like that. The starter/turn signal switch wires are fed straight through the headlight bucket to the main wiring harness so I can't short the ground without cutting the wire. I tried shorting the brown/black wire on the starter relay to ground but that doesn't crank the engine which leads me to suspect the starter relay rather than the ignition switch/wiring.

I popped open the relay thinking maybe it just needed to be cleaned but it looks pristine, and it also doesn't look like the pictures of r75/5 relays I can find online.
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Any clue how I can verify that the relay is the problem?

As I'm on the road I may have to just circumvent the relay for now but I'd prefer to fix it properly right away.