Inputs! You can cut RCA cables, splice 'em into the factory high level output, and run 'em into this amp... just don't forget to flip the switch to "high level" inputs. The amp is rated for up to 10 volts for the high level input. Maybe I'll try to get a reading with a digital multimeter... I guess I'd need to tap in to the line as it drives the speakers, and out the meter in A/C mode... Maybe it'll work (or maybe not)... but the reading would be the RMS... not the peak.