I tried to read about the ground issues recently. I could see the two right by the battery. Those are the easiest to clean obviously and seem like they could definitely be a problem if they got loose or dirty. I don't know if the left is referred to to as the main frame ground or not. The one on the right I am pretty sure is called the engine ground. There is also a fuse to the left of the battery that is obvious if you know it is there.
There is also a ground under the fuel tank where three wires share the same connection point. I thought that was a very suspicious area and would be worth checking. It was way easier than I thought it would be to lift up the tank. There were basically two bolts on the front and two on the back and the tank could be placed pretty far out of the way without disconnecting anything. This ground had three wires that sandwiched together and connected to a bracket. That bracket then connects to the frame. One mine, the bracket didn't seem too well connected and had quite a bit of residual paint.
The previously linked post mentions the ignition relay. I really thought that was something worth trying. This is a very common relay so you could probably get one locally. I am pretty sure my Chevy has one for the cooling fan. I sort of got suckered by this thread
https://www.spyderlovers.com/forums/archive/index.php/t-6755.html and got one at Napa for about $15. Advance, etc. list these cheaper ones, but my stores didn't show any stock. I think all bikes have this relay, but I am not 100% sure.
I also saw some rectangular ground junctions near the mirrors that were wrapped up. These didn't seem suspicious at all. They seem very solid and I wouldn't suspect a problem with them after looking at them.
What ultimately solved my problem was just pushing around on the wires under the gas tank with the key on. Pushing on the grounds under the tank would make the gauges move. I massaged wires and got super lucky because I hit a spot that would make the bike turn back on in the large loom on the left under the tank. That loom was very easy to unseal and inspect, but you would need to expect to be able to reseal it somehow with tape or adhesive.