Main Relay (Battery)
- Activated by ignition switch, the main relay supplies power to MCU and other computer-controlled systems. On 325i Series models, relay is located on left front shock tower. On 5 and 7 Series models, relay is located in relay block, behind right front strut tower. On 635CSi models, relay is located on outside of relay/fuse box on left side of engine compartment.
- Note wire colors and relay terminal identification. Apply battery voltage to both Red wire terminals of relay. Ground the Green wire terminal of relay. Voltage should now exist at the Red/Blue and Red/White wire terminals of relay. Replace relay if voltage did not exist.