You don't have to be an expert with the mm (multimeter) to do these simple tests. What I want you to do is test for 12v + at the amps main power input, and at the remote turn on input. Set your multimeter to dc voltage and for the proper range (12 volts). Then place your black probe ( negative) on the ground of the battery and your red probe (positive) on both of those terminals of the amp.
The positive terminal will show you 12v + no matter what position the ignition is in, it is a constant power source. The remote turn on, will show 12v + when the radio is turned on, sometimes techs will improperly install this wire to a ignition switched 12v +, so the remote wire will have 12v + whenever you turn the vehicle on instead of the radio. Either way, make sure both of those terminals on the amp show 12v + when the radio is on. Check those out and let me know what you come up with, then we will move on.