Quick answer
If you've got no sound after a headunit swap, it's often a missing remote turn-on, a loose integration harness or a mute wire grounded by mistake. Re-seat every plug, then confirm the amp wakes up per your build sheet.
Problem
- You've got no audio after wiring work or a headunit swap (general audio, not MK4-only).
Symptoms
- You get nothing on any channel or source.
- Or only the amplified channels are missing while the dash speaker still works.
- It started right after you put the trim back together.
Cause
- You've left Mute or “maximum startup volume” set to zero.
- Speaker plugs reversed on an adapter harness.
- Your Factory amp isn't waking, so the remote or LO doesn't match.
- Pinch or screw damage in the door boot.
Fix Step-by-step
- Prove the headunit outputs with a safe known-good speaker channel only where a technician approves. Otherwise stop at a visual inspection.
- Re-seat the harnesses, then confirm the amp remote turn-on if your build has one.
- Check the integration sheet in case you've grounded a steering-wheel mute harness by accident.