#9 to reducer, reducer to gauge. That's it. I believe the ignition switch will turn on the fuse panel and that will turn on the #9 gauge power wire. (that would be easy to test). Anyway: One end of reducer goes right onto the gas gauge power terminal. Crimp a ring tongue terminal onto #9 and screw it to the other end of reducer. There is no polarity on the gas gauge resistor/reducer. There are quite few a members who don't use a reducer and they have had no problems. It seems like cheap insurance to me.
Continuity testing is done with NO battery power connected. The multimeter provides a small current to pass thru the wire or component being tested to see if one thing is connected to another or to find both ends of a wire. Probably need to learn how to do that.
Testing for power, with power on, can be done with a ice pick style light tester, carefully. Nothing is dangerous or tricky. You just don't touch a hot wire to chassis ground. Always have the battery negative disconnected when doing wiring or replacing a component.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
