The electrical system of the Aermacchi Harley-Davidson X-90 from 1974, 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 1IgnitionThe black wire goes through the terminal block to the coil. Two wires go from the coil to the handlebar switch: black and brown.
Circuit 2LightingThe red wire feeds the handlebar switch. It sends the current to the headlamp through white or black. A red wire goes from the headlamp to the warning lamp.
Circuit 3Tail light and clocksThe yellow wire from the handlebar switch feeds the tail light and the speedometer lamp.
Circuit 4Stop lightThe green wire feeds the stop light. The two switches are in series: front via green, rear via green-black and then to earth.
Circuit 5HornThe handlebar switch feeds the horn with the red wire. The light blue wire goes back to the button.
Read this firstWatch out forUncertain colours and terminals
- This model has no battery. The generator feeds the lights directly.
- The inside of the handlebar switch is not shown in this diagram. Check with a meter which terminals are connected in each position.
- The book does not say which wire is high and which is low beam. Where this page does say so, it was worked out from the warning lamp. Check it at the headlamp.
- The book does not say how the horn button makes its earth. Check with a meter.
- This diagram is hard to follow in the photo. Where wires cross, the connection was worked out from colour and function. Check those connections with a meter.
- In the drawing two yellow wires go to the tail light. One comes from the speedometer lamp, the other from the handlebar switch.
- Bulbs according to the book: headlamp 20/20 W, tail light 5/18 W, warning lamp and speedometer lamp 3 W.
Our own drawings per circuit. The connections are based on the workshop manual for this model. Not an official publication of the manufacturer.