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The wiring diagrams, sometimes called Electrical Schematic Diagrams, for your airhead, will usually show the wire insulation color and the cross-sectional size (in mm) of the conductor. American wire gauge sizes are seldom used in vehicles in odd number sizes. American wire sizes are specified in GAUGE (ga), a different system of measurement. If you are replacing or installing wiring, use the same equivalent or next lower ga number (next larger size) as shown.

For other than the factory specified wire size and usage, you should know that the larger the expected current flow, the larger the conductor needs to be. The longer the run of wire, the larger the conductor needs to be.

0.5   metric is 20+ ga, use 20 ga
0.75 metric is 19 ga, use 18 ga
1.0   metric is 17 ga, use 16 ga
1.5   metric is 15 ga, use 14 ga
2.5   metric is 13 ga, use 12 ga
4      metric is 11 ga, use 10 ga
16    metric is   5 ga, use 4 ga

Diagrams on airhead schematics, colors:

BL blue...usually, not always, oil pressure, ALT (GEN) lamp;
             alternator
BR brown...always the ground, battery negative, frame ground.

GE yellow...low beam

GR grey(gray)...rear lights

GN green... usually, not always, ignition coil connection

RT   red...battery, and often from the light switch and ignition
               switch

SW black...usually, not always, the starter, and some functions to
               the ignition coil and starter

VI    violet

WS white...high beam

TR   transparent (not airheads)

If two colors are used on a wire, it is USUALLY shown with a hyphen, example: RT-GE

Two color wires MAY have some related function to the stripe color, or the body color, or both, or neither.

BOSCH codes:

**Note: These numbers/letters are found on all sorts of devices in your airhead, from sockets to coils. This is a comprehensive list, and it combines Bosch published codes AND the specifications in DIN72552, thus some listings will have 1 or more possible functions/devices. This list covers FAR more than that used on airheads. Note that sometimes there is a bit of ambiguity in actual use.

1     Ignition, coil, primary, breaker, low voltage, distributor
1a   If a dual breaker, #1
1b   If a dual breaker, #2
2     Ignition, switched ground, magneto
4     Ignition coil, ignition distributor, high voltage
             If two circuits, then 4a is coil 1 terminal 4,
             and 4 b is coil 2 terminal 4
15   +, primary, ignition coil, ignition switch output
15a output of ignition dropping resistor
17    glow plug of starter switch, start
19    preheat
30    from battery, + direct
30a series parallel switch, 12/24 volts, input, direct, from battery

31   battery negative (-), return line or ground, could be via switch
            or relay
32 to 33R   all are for series-parallel arrangements of battery 12/24
            volt switching, MANY functions.
32   return line, polarity reversed at 32, 33, possible
33   main return
33a self parking switch off
33b shunt field
33f second lower speed
33g third lower speed
33h fourth lower speed
33L CCW rotation
33R CW rotation
45    starter, separate relay, output, main current input
45a 2 starter parallel operation, output 1 and input 1 and 2
45b as above, output 2
48    starter and start repeat relay for monitoring starter
49    turn signal flasher, input
49a turn signal flasher, output
49b turn signal flasher, output, circuit 2
49c turn signal flasher, output, circuit 3
50    starter direct control
50a series-parallel, output of battery switch
50b series-parallel, 2 starters, sequential control
50c input, starter relay 1
50d input, starter relay 2
50e input, starter lock relay
50f   output, starter lock relay
51    + to light switch, alternator DC at rectifier.
51e alternator, as above, but with choke coil for day driving
52    trailer signals
53    wiper motor (can have -a,b,c,e,i functions)
54    brake stop light-directional light, trailer items
55    fog lights
56    lights, tach lights, headlights
56a high beam and high beam indicator
56b low beam (d is used for flasher contact)
57    parking light, side markers, -a is parking, L is left, R is right

58   lights...accessory, sidecar, rear. Also used for instruments,
              license plate lights, some side markers, and variable
              intensity functions
59    alternator a.c....and other functions specialized internally

61    indicator charge light
71    horns
72    alarm, emergency lights
75    radio, cigarette lighter
76    loudspeaker
77    door control
81-84    various styles of switches
85-86    switching relay
87-88    more relays
D-    dynamo
D+    + generator output, dynamo +
Df    field of generator, dynamo field, Df1 is #1, Df2 is #2
F      as above
B+   Battery +, + on regulator
B-    Battery negative (-)

Directional signals:
C      first indicator lamp
Co    maintain
C2    second lamp
C3    third lamp
L      turn signal, left
R      turn signal, right

revisions: