RCA cables carry the line-level audio signal between a head unit’s preamp outputs and an amplifier’s inputs. Despite carrying no more than a few volts at most, these cables are among the most noise-sensitive in the vehicle and deserve careful attention during installation.
The fundamental routing principle for RCA cables is to keep them as far away from power wiring as possible. Power cables carrying high currents generate electromagnetic fields that can induce hum into adjacent low-level signal cables. In practical terms, this means routing RCA cables along the opposite side of the vehicle from the main power run — if the power cable runs along the driver’s side, route the RCA cables along the passenger side.
When power and RCA cables must be in close proximity, crossing them at right angles minimizes the inductive coupling between them. Running them parallel for any significant distance, especially in close proximity, is the primary cause of alternator whine in car audio systems.
Cable quality matters, though not always in the ways marketing suggests. The most important qualities in an RCA cable for automotive use are good shielding (to reject externally induced interference), solid connector construction (to maintain a reliable contact over years of vibration), and correct pin polarity. Cables with 100% coverage braided shielding outperform those with foil-only shields in environments with high electromagnetic activity.
During installation, avoid sharp bends that could damage the cable’s internal construction, and do not coil excess cable length into tight loops — loops act as antennas and can induce hum into the signal. Instead, route the cable in gentle curves or cut it to the appropriate length.
Once installed, signal path integrity can be verified with a multimeter to confirm continuity and absence of shorts between the shield and signal conductor.