Operation & install location (what it does / where it lives): Used in multiple circuits such as horn, starter, fuel pump, ABS modulator, accessory power. Installs in the vehicle fuse/relay panel; location varies by platform (engine bay, passenger compartment, or trunk). Typical install: disconnect battery → pull old 5-pin relay (often marked 404/646) → seat new relay fully → reconnect and test circuit. (Audi EPC pages show these functions and locations, incl. “Position 404 & 646; passenger/engine/trunk compartments.”)
Compatibility — “Compatible with Audi A4” (years detailed for long-tail fitment): Compatible with Audi A4: 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024.
Compatibility — “Compatible with Volkswagen Golf” (years detailed): Compatible with Volkswagen Golf (incl. trims where equipped): 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021.
Complementary items: Often paired with high-note horn assemblies such as 5C0951223C (supersedes 1K0951223A/B) when restoring horn circuits; a 5-pin micro relay base/connector may also be needed for harness repairs. Verify by VIN/diagram for your vehicle.