1. The Key to Understanding Wiring Diagrams
Schematic Symbols
The Key to Understanding
Wiring Diagrams

2. Battery
Supplies a Direct Current (DC) source

3. Resistors impede the flow of electricity

4. SPST Switch (Single Pole Single Throw)
Opens (off) or closes (on) an electrical circuit

5. SPDT Switch (Single Pole Double Throw)
Switches from one electrical circuit to another

6. Light Bulb
Converts electricity into light

7. Fuse
Only allows a predetermined amount of current (AMPS) to pass through and if that amount is exceeded it will melt in half (open)

8. Capacitor
Blocks Direct Current (DC) flow, but allows Alternating Current (AC) to pass through

9. Diode/Rectifier
Allows current to flow through only one direction

10. Transistor
A solid-state electronic device that is used to control the flow of electricity in electronic equipment and usually consists of a small block of a semiconductor (as germanium) with at least three electrodes

11. Motor
Converts electrical energy into motion

12. Electric Fuel Pump FP
A motor driven pump, which supplies fuel to the engine

13. Chassis Ground
Connects the circuit to the metal body or frame of the vehicle using the body as a conductor in the circuit

14. (More commonly used than chassis ground)
Connects the circuit to the metal body or frame of the vehicle using the body as a conductor in the circuit
(More commonly used than chassis ground)

15. Relay OR
An electromagnetically controlled switch

16. Becomes magnetic when Direct Current (DC) is passed through it
Electromagnet
Becomes magnetic when Direct Current (DC) is passed through it

17. Light Emitting Diode
A one-way check valve for electricity that lights up when current is passing through

18. Variable Resistor
The resistance to the flow of electricity can be adjusted

19. Variable Capacitor
A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically. Variable capacitors are often used in L/C circuits (tuners) to set the resonance frequency, e.g. to tune a radio (therefore they are sometimes called tuning capacitors)

20. Transformer/Coil
The secondary induced voltage VS is scaled from the primary VP by a factor ideally equal to the ratio of the number of turns of wire in their respective windings:
By appropriate selection of the numbers of turns (N), a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.

21. Multi-position switch like the one used in the DVOM!
Rotary Switch
Multi-position switch like the one used in the DVOM!

22. Converts electrical energy into sound
Horn/Speaker
Converts electrical energy into sound