Main Relay (Battery)
- Activated by ignition switch, the main relay supplies power to MCU and other computer-controlled systems. On 325 Series, relay is located on left front shock tower. On 525i, 535i and 735i, relay is located in relay block, behind right front strut tower.
- 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 no voltage.