Hey, valve-adjustments are pretty advanced stuff, good job!!!
Yup, you found starter solenoid.
It's held onto bracket by rubber sleeve. Pull it towards back to remove from sleeve. Then at bottom, you can flip off rubber covers over the cable terminals. Then you'll see two big terminals to bridge. One of these connects directly to battery's +12v terminal, so be careful not to touch it to frame or any other wiring.
BTW, need to leave red plug connected as it provides power to ignition-switch.
