CB550 Electric Starter Install

So my bike has always been kick start only bike but i recently decided to install electric start.
2 questions

- i purchased the motor but it only has one wire going into it... is this the power or ground? if its ground where is the power?

- ofcourse stock starter solenoid/ relay would work but nothing is stock on my bike at this point. are there more reliable/ cheaper starter solenoid options out there?

It's a power wire and connects to the solenoid.

The motor is grounded through the engine.

Just about any solenoid will work. A quality one will work for longer, though.