Quick answer
No audio with a retained factory amplifier is most often missing remote turn-on or data wake, or feeding line level where the OEM amp expects high level (or the reverse). Match turn-on and signal type to your integration sheet before blaming speakers.
Problem
- Factory amplifier must stay in the chain on some vehicles.
Symptoms
- No audio after headunit swap.
- Amp never wakes; faint hiss only.
Cause
- Factory amplifier turn-on, integration, or high-/low-level feeds do not match the new headunit outputs.
Fix Step-by-step
- Confirm remote turn-on or data wake per integration sheet.
- Match high-level vs line inputs to what the factory amp expects.
- Retain steering mute leads if the vehicle uses them.
- Verify fuses on factory amp feeds.