Morning Stu
If this is for your Angel Eyes on the S53 I took a power feed from the where the ECU lives take off the lid and where the loom connects 3rd wire from the left is Red/white trace, earth I used the Headlamp earth so only running a single wire for power. This power feed is ACC switched but remains live for 20 secs after key out. You can test by sticking a pin into the wire and using a tester
Dave