Tell us which way you went. I hooked mine to the battery and it's worked great for years and years. Never even considered going to the starter solenoid and ground off the tranny. Let us know.
Dont quite understand Your Question About which way I went. Got the idea about using the starter solenoid from Charging Welding Machine Batteries when I couldnt get to the batteries on the machine. So I used the starter solenoid, which also works well on my bike. Besides I dont like extra wires coming out of My bike.