The 12 volt electrical system of the Aermacchi Harley-Davidson Sprint SS and SX from 1973, with starter motor and turn signals, drawn circuit by circuit. Each wire is labelled with its colour.
Always check a wire with a multimeter before you connect it, and disconnect the battery first.
Circuit 1Power from the batteryThe positive goes through the fuse to terminal 1 of the ignition switch, and with a red wire to the red terminal 88 of the starter relay. From there a red wire runs to terminal 7. The negative goes to earth.
Circuit 2ChargingThe alternator supplies the rectifier-regulator. With the lights on, the switch (terminals 8 and 9) adds the green wire. The warning lamp sits between terminal S and the power after the ignition switch.
Circuit 3StartingThe start button energises the relay. The relay sends the heavy current to the starter motor.
Circuit 4IgnitionTerminal 6 feeds the coil after the ignition switch. The points switch the coil, and the coil gives the spark to the plug.
Circuit 5LightingTerminal 4 feeds the handlebar switch when the lights are on. It selects one filament or the other.
Circuit 6Tail light and clocksThe yellow wires feed the tail light and the instrument lamps, also in the park position.
Circuit 7Stop lightBoth stop light switches get power after the ignition switch. Either one is enough to light the stop light.
Circuit 8HornThe horn gets power after the ignition switch. The button in the handlebar switch makes the earth.
Circuit 9Turn signalsThe relay keeps interrupting the current. The handlebar switch selects right or left.
BulbsWhich bulb goes whereRating and part number for this model
| Lamp | Rating | Part no. |
|---|---|---|
| Headlamp (sealed beam) | 30/30 W | 67716-73 |
| Tail and stop light | 3/32 cp | 68165-64 |
| Turn signal | 21 W | 68556-73P |
| Speedometer, rev counter, high beam and turn signal warning lamps | 3 W | 71090-64 |
| Generator warning lamp | 1.5 W | 71092-73P |
Note: the bulb table gives 30/30 W for the headlamp. The key of this diagram gives 35/35 W. Check what is fitted to your bike.
From the bulb table in the workshop manual. These are old Harley-Davidson part numbers. cp stands for candlepower, the old unit of light output.
Read this firstWatch out forUncertain colours and terminals
- This is a 12 volt system with an alternator and an electric starter.
- There is one 25 amp fuse, at the battery.
- The jumper between terminals 1 and 5 of the ignition switch gives the park position power without the ignition on.
- Where wires disappear into the loom, the connection was worked out from colour and function. Check those connections with a meter.
- Switch table in the book: ignition 1-2 and 6-7, ignition and lights 1-2-3, 4-5, 6-7 and 8-9, park 5-10.
- The starter relay terminal numbers are hard to read. They are shown here as 85, 86, 88 and 88a, as on the SS and SX 350. Check them on the relay.
- The horn feed wire has no colour code in the drawing. That is why it says "colour?". Check with a meter which wire it is.
- At the handlebar switch there is another blue wire that cannot be traced. It is probably earth. Check with a meter.
- After the wiring connector the wires to the turn signals are black.
- Two-colour wires are drawn with the second colour as a dashed tracer.
- The rev counter lamp is fitted to the SS only.
Our own drawings per circuit. The connections are based on the workshop manual for this model. Not an official publication of the manufacturer.