Remove your grounds to the frame and to the engine and clean the terminals and the mount points you want fresh metal to metal and use some dielectric grease on these areas when reassembling. The shop manual for the cb650 is available and should show you the grounding locations if the exploded diagrams in the parts ficsh (do they still call them that?)
You are getting feedback in your circuit that. Sounds like it is trying to find a ground. A circuit with ground problems with find alternate paths to ground back feeding through cirvuit that share a gound point. Some devices or circuits have protection when they could be damaged by reverse polarity. But that is not the case on old bikes and cars...most circuits were unaffected negatively, as are our bike, by negatively I am referring to damaging components within that device. Exceptions are the voltage regulator, sometimes they fry if you were to reverse polarity the battery terminals. This is also true for a car battery even on old cars. You can only idiot proof things so much, you cannot protect against all idiots, they find new ways unaccounted for...
New repro harnesses are out there as well for the cb650 and not too expensive.
As far as your blinkers, they only work if bike is running. Also, is your blinker relay original or did you replace it with a new electronic flasher compatible with LEDs and incandescent bulbs that does not care about the load?
If you replaced it, then what model and brand flasher did you use?
Have you taken every connector apart one at a time and cleaned each and every terminal one by one with a brass brush in the barrel (female) and on the plug ( male) and then reassembled or reassembled with a tiny bit of dielectric grease on the male plug. You likely will need to use a spritz of spray electronics cleaner on the connectors before brushing if they previously had dielectric or other grease.
This is an important step to do on any new bike and periodically during your ownership, an every two year cycle at least is my practice on old bikes.
On a certain marque of car that is shunned by many and causes outcries that will remain nameless, 😉😁, it was good maintenance practice to clean the cabin fuse box every year. Moisture and open terminal design and dissimilar metals between brass fuse terminals and the metal of the fuses would cause interesting things to occur if neglected. It was a simple half hour job after you disconnected the ground of the battery with your brass brush. It was better to just change out all the fuses, provided you were not buying them at the dealer, rather than trying to clean the fuse ends. They were bullet shaped/pointed, on both ends, a certain germanic design.
