relay R4 and fuse number 2 looks after that meter and believe it or not the power supply to switch the relay on and off (terminal 86) comes from the abs control computer from pin 32 via the ABS pedal travel sensor/brake light switch theres a normal earth through terminal 85.you should have battery voltage at terminal 87 which is fused by fuse #2, and terminal 30 supplies the voltmeter
hope all that makes sence to you