The factory Harley radio does not provide RCA (low level) outputs and only provides speaker (high level) outputs. The harness has the RCA's to connect to an amplifier once the LOC (Line Output Converter) is connected. Without the LOC connected, there would not be any signal between the radio and the RCA's. Hopefully this answers your question.
The wiring harness has rca. So why the line in converter
The factory Harley radio does not provide RCA (low level) outputs and only provides speaker (high level) outputs. The harness has the RCA's to connect to an amplifier once the LOC (Line Output Converter) is connected. Without the LOC connected, there would not be any signal between the radio and the RCA's. Hopefully this answers your question.