What things mean in the world of Audi/VW wiring diagrams
                                                   These basic circuit numbers also correspond with the numbers found on the relay

15 = Powered when ignition is in "ON" or "START" position. Most common wire color: BLACK (BK)

X = Load-reduction circuit, powered by load reduction relay when ignition is in "ON" or :START" position. Most common wire color: Black/Yellow (BK/Y)

30 = Battery positive ( + ) Voltage. Powered whenever battery is connected. Most common wire color: RED (R)

31 = Ground (GND) or battery negative ( - ). Most common wire color: BROWN (BR)

50 = Powered only when ignition switch is in the "START" position. Most common wire color: RED/BLACK (R/BK)

B+ = From generator (GEN) or alternator (ALT) Charging Voltage to battery. Most common wire color: RED (R)

D+ = Generator (GEN) or alternator (ALT) warning light and field energizing circuit. (mostly associated with a (BATT) light). Most common wire color: N/A (Not Applicable)

85 = Ground (GND) (- negative) side of switching relay. Most common wire color: BROWN (BR)

86 = Power-input (+ positive) side of switching relay. Most common wire color: N/A

87 = Relay change-over contact.

When a color code is given on a wiring diagram, the first color is the dominant color. The second color is the secondary known as a "tracer" For example, the Load Reduction relay mentioned above will have a Black wire with a Yellow tracer or stripe on it.