Voltage drop and lights dimming above idle. I'm stumped....

Hello, I'm new to the forum and looking fwd to exploring all the info here!

I'm having a strange issue on my Formula 583 Deluxe. It initially started with a dead battery and a cooked voltage regulator.

I got a new battery and regulator and now anytime I go above idle, my lights go dim and the Tach stops working. Measured voltage at the lights goes from about 11v AC at idle and drops to about 7v AC.

I've tried the following to troubleshoot:

• I've replaced the battery and I have tried 2 different voltage regulators without any change.
• The lighting coil outputs 20v at idle and goes to over 40v at higher rpms...so the stator I'm thinking looks ok? I also measured the resistance at the coil and it's within spec for this model. I also didn't see any continuity between the AC output and the engine chassis.
• I've even added a ground wire from the chassis to the engine in case there wasn't a good connection.
• I've disconnected every harness under the handlebars I can find to see if something is causing a short. I haven't seen any difference in the behavior. I've also disconnected the entire hood harness and no change.
• I've tested both new regulators as per the rmstator youtube video.....both appear to be in working order
• If I test with the battery disconnected the voltage at the lights does the same thing...however the volts are about 6v at idle and drop to 3v when under throttle

I'm looking for some advice on what else to check. Both regulators have been Kimpex brand and I can't find OEM. But I can't imagine it's two bad regulators? What else could be causing the voltage to drop above idle?

Hoping someone has seen this before and can offer some additional advice...I'm stumped

Thanks in advance for your help!