Automotive Electrical Symbols
Automotive electrical symbols are the standardized shorthand of a wiring diagram: a battery, a ground, a fuse, a relay, a diode each has one drawn shape, and reading a schematic is just translating those shapes back into a real circuit. Get the symbols right and a diagram tells you where current should go — and, when something's dead, where it isn't going. This guide draws each common symbol, explains what it means, and flags the ones techs misread on the ASE A6 test.
Power and ground
Every circuit starts at a source and ends at a ground. Note that there are two ground symbols — they don’t mean the same thing, and the difference matters when you’re tracing a dead circuit.
Battery
Stored DC voltage source. Long line = positive (+), short line = negative (−).
Ground (earth/signal)
The 0 V reference and common return path. Decreasing bars.
Chassis ground
Ground through the body/frame metal — note the hatching, not bars.
Circuit protection
The fuse is the deliberately weak link: it opens before the wiring does.
Fuse
Sacrificial link that opens on overcurrent to protect the circuit.
Switches, relays, and coils
These control where current goes. A switch makes or breaks one circuit; a relay uses a small current to switch a bigger one; a solenoid turns current into a magnetic pull.
Switch (open / SPST)
Opens or closes a circuit. Drawn here open (normally open).
Relay
An electromagnetic coil that switches a separate, often higher-current, circuit.
Solenoid / coil
A winding that becomes an electromagnet when energized.
Loads and passive parts
Loads are what the circuit is for — the lamp, the motor. Resistors and capacitors shape the current on the way there.
Lamp / bulb
A lighting load — a circle with an X (the filament).
Motor
Converts current into motion — a circle with “M”.
Resistor
Fixed opposition to current flow (zigzag = US style).
Variable resistor / rheostat
Adjustable resistance — an arrow drawn through a resistor.
Capacitor
Stores charge; blocks DC, passes AC. Two parallel plates.
Semiconductors
A diode is a one-way valve; an LED is a diode that lights up. Direction is everything here.
Diode
One-way valve — current flows toward the bar, blocked in reverse.
LED
A diode that emits light — note the two arrows pointing away.
Wire connections — the marks people misread
This is where careful reading pays off. Whether two lines on a page represent one electrical node or two separate ones comes down to a single dot.
Connected wires (junction)
A solid dot = the wires are electrically joined.
Crossing wires (not joined)
A hop (or simply no dot) = the wires cross without connecting.
Connector
A separable plug/socket joining two wires or harnesses.
Junction (a solid dot)
- The crossing wires are electrically joined
- It's one electrical node
- Voltage here appears on both wires
Crossover (no dot / a hop)
- The wires cross but do NOT connect
- Two separate electrical nodes
- A fault on one doesn't reach the other
The call: When two wires cross on a schematic, look for the dot before you assume anything. Dot = joined; no dot (or a little arc) = they just pass each other.
Symbol misreads that cost points
| The symbol | What it actually means | The trap |
|---|---|---|
| A dot at a wire crossing | The wires are joined — one electrical node | No dot means they cross but do NOT connect; don't invent a connection. |
| Hatched ground vs. barred ground | Hatching = chassis/body ground; bars = signal/earth ground | Reading the wrong one sends you tracing the wrong return path. |
| A diode's triangle direction | Current flows toward the bar only | The bar is the 'stop.' A backward diode blocks the circuit — direction is the answer. |
| A switch drawn open | It's shown in its resting state, not in operation | Diagrams show the at-rest state; a normally-closed switch is drawn the other way. |
| Relay coil vs. plain coil | Relay = coil that switches a second circuit; solenoid = coil that makes a magnet | Both are windings — what they control is the distinction being tested. |
How symbols show up on the A6 test
The ASE A6 Electrical/Electronic Systems test isn’t a symbol-naming quiz, but it leans on these constantly: a large share of the questions hand you a wiring diagram and ask you to read it back to a fault. If you misread a junction as a crossover, or a chassis ground as a signal ground, you’ve mis-mapped the circuit before you’ve measured anything — and the voltage-drop or open-circuit answer that follows will be wrong for a reason that has nothing to do with your diagnostic skill.
So the reading order on a diagram question is always the same: identify the source and the ground, confirm which wires are actually one node, follow the current path through the protection and control devices to the load, and only then reason about where the fault has to be.
On a wiring diagram, one wire from a switch branches to two bulbs, and each branch has its OWN ground symbol. One bulb is dead; the other works normally. Reading the diagram, where do you look first?
- A The switch
- B The shared feed wire
- C The dead bulb's own ground branch✓ correct
- D The battery
Let the diagram narrow it for you. Everything upstream of the branch — battery, switch, the shared feed — serves both bulbs, so a fault there can’t leave one bulb working. Because the schematic shows each bulb with its own ground, the dead bulb’s fault has to be downstream of the split: an open in that bulb, its socket, or its individual ground path. The working bulb is your proof the shared part of the circuit is fine.
Exam trap: The switch, feed, and battery are shared, so a fault there would kill BOTH bulbs. Only the dead bulb's own branch — its socket or its individual ground — can take out just one.
Quick check
On a schematic, two crossing wires are drawn with a solid dot at the intersection. That means:
Once the symbols read automatically, the rest of A6 is diagnosis. Build from here with the A6 Electrical test guide, the wiring, grounds & relays reference, and the electrical & HVAC study pillar.
Frequently asked questions
What do the symbols on a car wiring diagram mean?
Each symbol is a standardized drawing of one component: a battery (long/short lines), a ground (decreasing bars or hatching), a fuse (a link in a box), a switch (a hinged line), a relay (a coil that switches another circuit), a diode (a triangle pointing at a bar), a lamp (a circle with an X), and so on. Reading a diagram is translating those shapes back into the real circuit and following the current path.
What's the difference between a chassis ground and an earth/signal ground symbol?
Both mean 'return path to 0 volts,' but they're drawn differently and point you to different places. The earth/signal ground is three decreasing horizontal bars; the chassis ground uses angled hatching to show the return runs through the vehicle's body or frame metal. Mixing them up sends you hunting the wrong ground.
How do you know if two wires on a schematic are connected?
Look for a solid dot at the intersection. A dot means the wires are electrically joined (a junction). No dot — or a little hop where one wire arcs over the other — means they cross but do not connect. This single detail changes how the whole circuit reads.
Which way does current flow through a diode symbol?
Toward the bar. The diode is drawn as a triangle (the arrow) pointing at a line (the bar); current passes in the direction the triangle points and is blocked in reverse. A diode installed or read backward effectively opens the circuit.
Why do I need to know electrical symbols for the ASE A6 test?
Because A6 hands you wiring diagrams. A large share of the Electrical/Electronic Systems questions ask you to read a schematic back to a fault — which means you first have to read the symbols correctly. Misreading a junction, a ground type, or a diode's direction leads you to the wrong answer before you've even started diagnosing.