Use this article if…
- Your headunit never switches to camera in reverse (any aftermarket unit), not “the camera page opens but stays black.”
- If your picture is black after it switches → Black / wrong picture or MK4 reverse black screen.
- MK4, no switch at all → MK4 no reverse display. Sense wiring → Reverse trigger wiring.
Quick answer
If reverse never switches, your headunit isn't seeing a reverse trigger. Check your reverse lamps work, then measure the trigger wire at the radio end while someone selects reverse. On a PVS MK4 that's pin 5 (BACK_CON) on the 16-pin main plug, and the wire is pink.
Problem
- Your reverse gear doesn't switch the display to the camera input.
Symptoms
- Your reverse lights work but the screen stays on radio or map.
- You see “no signal” or a timeout in diagnostics.
- It worked until you put the trim back on, now it's intermittent.
Cause
- No trigger to the headunit, the reverse-on wire is missing or wired wrong.
- Factory Toyota camera: you've got no trigger wire to connect at all. Reverse arrives on Connector 3, so a missing trigger isn't the fault to chase on that setup.
- PWM or filtered tail circuit, your meter shows odd voltage and the headunit never sees a solid +12.
- Wrong input selected in the headunit, you're on camera 2 instead of camera 1.
- Fuse or join failure at the rear harness.
Fix Step-by-step
- Check your reverse lamps light up, then measure the trigger wire at the headunit end in reverse with the parking brake set and conditions safe.
- On a PVS MK4, the reverse trigger is pin 5 (BACK_CON) on the 16-pin main plug, and the wire is pink on all recent batches. If yours is brown, that's an earlier build, not a fault.
- If the trigger is unreliable, re-run it to your integration sheet. A dedicated body pin or relay output is usually cleaner than a splice.
- In headunit settings, assign the correct physical port to “reverse camera”.
- Boot-cycle, then test in Park and Drive where that applies.