The single black that exits the group of wires coming from the flywheel, about half way up, is only used for testing the ignition and is otherwise left well alone.

The white is only used to "boost" the charging and is not normally used.

Thanks for clearing that up!

At the risk of more confusion lol....glad you found where the black grounds plug. Now your looking for a brown for signal on one side of the bike and dark green to operate the other side. Your not looking for a white. Brown and dark green are the hots for the signals in the headlight shell and main harness near the oil tank. You have to have the key on and a good battery when you operate the flasher.

No, I think everyone is clear! I do have a good battery and intact wiring harness. Some parts were just hidden with zip ties, etc.
I checked continuity with my multi meter (good wires)but still not getting power to the signals. Will I still get constant power if the flasher relay is bad? No voltage to the bulbs.

The flasher relay has to operate to get voltage to the bulbs. With key on and good battery listen for any noise at the flasher when you activate the signals. If nothing be sure and check the 10 Amp main fuse. If you tried the signals with green or brown bare wires or connectors touching each other or the frame then you could have blown the fuse. Only one fuse one the old bikes.

Further to my previous reply, there should be a short black wire that loops on the stud under the battery box where the indicator relay mounts, and connects to a black male coming out of the main harness in that area. I don't have photos of mine, but this parts diagram night help - see item number 11.

yamaha-rt3-1972-1973-usa-electrical_bigyau1202e-11_0274.gif (1092×1500) (cmsnl.com)

Here's a pic of what GR8UNCLEAL's referring to above:

Thanks for the diagrams and info. I’m getting really close to having everything “sorted”. The remaining issue is the headlight, I’m still checking that circuit to run down the issue.

Headlight only works with engine running and ignition switch in the second click round.

Great uncle Al, thanks for the info about the headlight only coming on with the engine running! I may be troubleshooting a problem that doesn’t exist, hhmmm.
With a hot battery and the key switch in the far clockwise position I only have six volts at the brown wire, I was thinking the yellow and green should be hot to power the high and low circuit to the headlight?
Not sure if I have a problem but don’t want to put the bike together to start and check with the engine running.