Every circuit on paper is a loop. Here is how to follow it.
A wiring diagram is a map of a circuit. Once you know the symbols, it tells you where to look when something stops working.
1. Common symbols
| Symbol | Means |
|---|---|
| Long and short parallel lines | Battery or cell |
| Circle with a cross | Lamp |
| Zigzag or rectangle | Resistor |
| Gap with a hinged line | Switch |
| Coil and switch in a box | Relay |
| Small S-shape in a box | Fuse |
| Triangle with a bar | Diode |
| Downward lines or a triangle | Earth |
| Dot where lines cross | Joined wires |
2. How to trace a circuit
- Start at the battery positive.
- Follow through the fuse, then the switch or relay.
- Find the load.
- Follow the return path back to earth or the battery negative.
If any part of that loop is broken, the load won't work.
3. Wire colours and labels
Manufacturer diagrams usually label wire colours and connector pins. Learn the legend first. Colours vary between makers, so never assume.
4. Use it with your meter
Mark test points on the diagram. Check for voltage at each point along the path until you find where it disappears.
5. Quick summary
- Learn the symbols.
- Trace positive, through protection and control, to the load, and back.
- Use the diagram to choose test points.
240V AC mains can kill. In Australia, work on household mains wiring must be carried out by a licensed electrician. Low-voltage DC can still deliver very high current, so treat batteries with respect.
