Quick answer
If your picture got worse after you lengthened the run, it's usually a cheap extension, a loose barrel or coax running parallel to winch and charge cables. Use proper video coax, re-seat any joint that's exposed to weather, then reroute crosses at 90° away from high-current paths.
Problem
- You're extending camera coax, or chasing a flaky picture from a long run.
Symptoms
- Your picture got worse after the extension.
- Your picture cuts in and out when the doors or tailgate move.
Cause
- If you add adapters or run a long length, shield continuity weakens and noise couples in.
- Vibration at the hinges works a marginal barrel connector loose, so you lose the picture on and off.
Fix Step-by-step
- Use a proper video extension, not random RCA run as speaker wire.
- Keep the coax away from alternator charge leads and winch cables.
- Re-seat the barrels, then check for water behind the plate.
- Use dielectric grease only where the manufacturer allows it.