OK if you dmm is broke your gonna need one. But if you set the dmm to read OHMs you can take the reading of either speaker and see if there correct or not. YOur reading will depend on the ohm of the speaker.Unplug the speakers from the amp or speaker terminals. Put red to red bblack to black. The voltage to the amp is checked by putting the red to positive post on amp, and the black on the ground. Now turn it up and watch the voltage, if it ever dips under 12.4 your amp is most likley gonna be frying out soon. Mosfets dont like voltage drop and this creates alot of exxcess heat. all of a sudden youll get the magic smoke