Definitely check the fuse first.
The voltage comes from the HUD to the PCM. The PCM sends 4000 grounds per mile. The HUD senses voltage drops.
You can test the wire at the PCM for voltage. Disconnect the green wiring harness. Look into the plug with the clip on the top and the wires in the back.
Ignition on (engine doesn't have to be on)
Second row, terminal No. 7 should have a dark green and white wire hooked to it. Test the voltage at the dark green and white wire by connecting a voltmeter to it (and the other side of the voltmeter to ground)
Should be 12V coming from the HUD.
1999 540iA Sport
Former 93 SSEi Owner
Former 89 SE Owner