Totally bizarre electrical issue...see video

I'm rebuilding a '72 Honda CB450 K5, and am 99% done. However, I'm having issues with the electrical. I got the bike to start but then suddenly died and oddly the starter switch, horn switch and neutral light (in the tach) all went completely dead. Headlight, tail light and turn signals all work perfectly fine.

While trying to trace the issue I discovered that if I unplugged the two horn wires and directly ground the ground (green) wire to the engine or frame, and took the lead wire (black) and connected it directly to the battery it would "reset" the whole system and everything would work...starter switch, horn, neutral light all work fine and bike will start. Then it will go dead with the same problem. It's ultra odd because when connecting the lead wire to the battery I have to first touch it to the negative terminal, then to the positive terminal. After doing that current will run to the horn. I can then plug the horn wires back into the harness and everything will work...until it doesn't and I have to do the whole process over again.

Bike is basically stock but does have a SparckMoto regulator/rectifier and a brand new ignition switch.

What could be causing this? Video is below

https://youtu.be/BBGHSkL3FSM

Go back through and check all your grounds, back of the headlight, and oddly enough, I don’t know what kind of handlebars you’re running, but some of CB’s handlebar switches clamped around a grounding/locating lug on the stock bars. I came across this issue a few times.


Sent from my iPhone using Tapatalk

Sounds a lot like a grounding issue to me. Almost all problems involving strange behavior over multiple circuits end up being an issue with the grounds. Make sure you battery has a good solid connection from the negative terminal to the frame and that all your ground wires also have good connections.

If all of that checks out, we can start looking at each circuit step by step. Is the harness OEM?