Best way to check my Power & ground to the Amp?

That sounds ok, but you would probably want to check the amperage,which actually is what it sounds like you did. You know the E=I/R I ume, so you couldplug in the numbers to see. If you want resistance, just run the DMM on ohms and see what you got. Since the power and ground are conductors, you should have very little resistance, so what your doing seems almost futile in regards to how the system sounds. I would look at what size conductor/wire your running, either 8, 4 or 0/1 cable, and then check the ground for ohms of resistance from the terminal end to the metal its connected to, but as long as it's grounded it probably would not make a difference. Seems your worried about nothing when the gage of the wire is what you should be looking at.. A 1" hose will flow a hell of a lot more water than a 1/2" hose...