Fleet electronics terms, A to Z, in plain language.
Accelerometer. A sensor inside a tracker or camera that measures motion in three directions. It's how the platform detects harsh braking, hard cornering, rapid acceleration, and impacts.
Accessory (ACC). The key position between OFF and RUN. A wire that shows 12 volts in ACC and RUN but drops during CRANK is an accessory wire, not an ignition wire.
ADAS. Advanced Driver Assistance System. Camera-based features such as forward collision warning, lane departure, and following distance alerts. Some fleet dash cameras include ADAS.
Aftermarket. Any part or device not installed by the vehicle manufacturer. Everything we install is aftermarket.
Alternating Current (AC). Current that reverses direction many times per second. Wall power is AC. Vehicles run on DC.
Alternator. The belt-driven generator that charges the battery and powers the vehicle's electrical system while the engine runs. Normal charging voltage is 13.5 to 14.8 volts.
American Wire Gauge (AWG). The standard for wire size. Smaller number, bigger wire. 18 AWG is thin, 10 AWG is heavy.
Ammeter. A meter that measures current in amps. A clamp-on ammeter measures without cutting the wire.
Ampere (amp, A). The unit of electrical current, the rate of flow. Most tracker and camera devices draw well under 1 amp while running.
Anode. The positive end of a diode. Current goes in the anode and out the cathode.
APN. Access Point Name. The cellular network setting that lets a tracker's SIM card connect to its carrier. Usually preset by the device maker; occasionally needs to be entered manually.
Asset tracker. A battery-powered or solar-powered GPS unit for trailers, equipment, and containers that have no vehicle power. Reports less often than a wired tracker to save battery.
Auxiliary input (AUX in). A wire on a tracker or camera that senses an on or off signal from the vehicle: door open, PTO engaged, salt spreader on, and so on.
Auxiliary output (AUX out). A wire on a tracker that switches to ground or to positive on command. Used to drive a relay for a starter interrupt, a buzzer, or a lamp.
Back-probe. Testing a circuit by sliding a fine pin into the back of a connector alongside the wire, so the meter reads the circuit without piercing insulation.
Battery. The 12 volt lead-acid (or AGM) source that starts the vehicle and powers everything when the engine is off. Heavy trucks use two or more batteries in parallel, still 12 volts.
Body Control Module (BCM). The computer that runs body functions: door locks, lighting, windows, chimes. Often the module that sets codes when a test light is used incorrectly.
Bus. See Data bus.
CAN bus. Controller Area Network. The two-wire (CAN High and CAN Low) data network used on every modern vehicle. Trackers read engine data from it. Never cut or splice it.
Cathode. The striped end of a diode. Current flows out the cathode.
Chassis. The metal frame or body of the vehicle. Chassis ground means a ground connection to that metal.
Circuit. A complete path for current: from the source, through the load, and back.
Clamp-on meter. An ammeter that measures current by clamping around a wire. Used to find parasitic draw.
Closed circuit. A circuit with a complete path. Current flows.
Coil. A winding of wire that creates a magnetic field when current flows through it. The coil in a relay pulls the contacts closed.
Conductor. Any material that carries current easily. Copper wire, the vehicle body.
Constant 12 volt. A wire that shows 12 volts at all times, key on or off. Also called battery or B+.
Continuity. An unbroken path between two points. The beeper setting on a meter tests it.
Crank. The key position (or push-button state) that turns the starter. A true ignition wire holds 12 volts during crank.
Current. The flow of electricity, measured in amps.
Dash cam. A camera mounted at the windshield that records the road, the driver, or both. Fleet dash cams upload clips to the platform on events such as harsh braking or impact.
Data bus. Any single wire or wire pair that carries many signals as digital messages instead of one wire per function. See the Data Bus chapter.
Deutsch connector. The round sealed connector used on heavy trucks. The 9-pin version carries J1939. Black is 250 kbps, green is 500 kbps.
Digital Multimeter (DMM). The meter that reads volts, ohms, and continuity. The only safe way to test circuits on a modern vehicle.
Diode. A component that lets current flow one way only. See the Diodes chapter.
Direct Current (DC). Current that flows in one direction. Vehicle electrical systems are 12 volt DC (24 volt on some heavy equipment and buses).
Door trigger. The wire that changes state when a door opens. Negative on most vehicles, positive on some Ford and older Chrysler products.
Driver ID. A way for the platform to know who is driving: a key fob, an RFID card, a phone app, or the camera's face recognition.
DTC. Diagnostic Trouble Code. A stored fault code. See the Codes chapter.
ELD. Electronic Logging Device. A federally mandated device that records hours of service for commercial drivers. Must be connected to the engine bus to read engine hours and odometer.
Engine hours. Total running time of the engine, read from the bus. Used for maintenance scheduling.
Event. Anything the platform flags: harsh braking, speeding, geofence entry, impact, idle over a limit.
Fail-safe. A design where a failure leaves the vehicle able to operate. A starter interrupt wired through a relay's normally closed contact is fail-safe.
FMI. Failure Mode Identifier. The second half of a heavy-truck fault code. See the Codes chapter.
Fuse. A component that burns open when current exceeds its rating, protecting the wire. Sized to the wire, not the device.
Fuse tap (add-a-circuit). A plug-in adapter that takes power from an existing fuse slot and adds a second fused circuit.
Fusible link. A short length of special wire that acts as a fuse for high-current circuits, often near the battery or alternator.
Gauge. Wire size. See AWG.
Geofence. A boundary drawn on the platform map. The platform alerts when a vehicle enters or leaves it.
GPS. Global Positioning System. The satellite network trackers use to find location. Needs a view of the sky, so antenna placement matters.
Ground. The return path for current, connected to the vehicle's chassis and the battery negative.
Ground loop. Noise or false readings caused when two devices are grounded at different points with a voltage difference between them. Fixed by grounding to the same clean point.
Grommet. A rubber ring that lines a hole in metal so wire can pass through without chafing.
Harness. A bundle of wires with connectors, made for a specific device or vehicle. A vehicle-specific harness plugs in without splicing.
Harsh event. Harsh braking, harsh acceleration, or harsh cornering as measured by the accelerometer.
Hardwire. Connecting a device to constant, ignition, and ground by splicing, rather than plugging into the OBD port.
Heat shrink. Tubing that shrinks when heated to insulate and seal a splice.
Hertz (Hz). Cycles per second. Rarely matters in our work except for bus speeds (kilobits per second).
Idle time. Engine running, vehicle not moving. One of the top items fleet managers watch. Read from the bus or inferred from ignition plus GPS.
Ignition (IGN). The wire that shows 12 volts in RUN and holds during CRANK. Tells the device the vehicle is on.
Immobilizer. A factory anti-theft system that prevents starting without the correct key, or an aftermarket starter interrupt controlled by the tracker.
IMEI. The unique serial number of a cellular device. Every tracker has one. It's what the platform uses to identify the unit.
Impedance. Resistance to AC or signal current, measured in ohms. Mostly an audio term, but it comes up in speed-signal taps.
Inductor. A coil. Stores energy in a magnetic field. A relay coil is an inductor, which is why it kicks back a voltage spike.
Insulation. The plastic coating on wire that keeps current in the conductor.
J1708 / J1587. The older, slower heavy-truck data bus, found on trucks before about 2007. Uses a 6-pin Deutsch connector.
J1939. The CAN-based heavy-truck data bus. Uses the 9-pin Deutsch connector.
Key-off draw. See Parasitic draw.
Kick panel. The trim panel beside the driver's or passenger's feet. Common spot for the BCM and for hiding a tracker.
Latching relay. A relay circuit that stays energized after a momentary trigger until it's reset. See the Relays chapter.
LED probe. A low-current test light with red and green LEDs for positive and negative. Safe on modern vehicles.
Load. Whatever uses the current in a circuit: a lamp, a motor, a device.
Loom. Split plastic tubing that protects and hides wire runs.
Multiplexing. Sending many signals on one wire. See Data bus.
Multimeter. See Digital Multimeter.
Negative trigger. A signal that switches to ground to activate. Most device outputs and most door triggers are negative.
Normally Closed (NC). A relay contact that is connected at rest and opens when the relay energizes. Pin 87a.
Normally Open (NO). A relay contact that is open at rest and closes when the relay energizes. Pin 87.
OBD-II. On-Board Diagnostics, second generation. The 16-pin port under the dash on every light-duty vehicle since 1996. Provides power, ground, and the CAN bus.
Odometer. True vehicle mileage read from the bus. More accurate than GPS distance.
Ohm (Ω). The unit of resistance.
Ohm's law. Volts = Amps x Ohms.
Open circuit. A break in the path. No current flows.
Parasitic draw. Current a device pulls with the key off. A tracker in sleep mode should draw only a few milliamps. Too much drains the battery.
Pigtail. A short length of wire with a connector on one end, used to connect to a relay socket, a fuse tap, or a harness.
Pin out. A diagram showing what each pin in a connector does.
Platform. The web or phone software where the customer sees their vehicles. Also called the portal or the dashboard.
Polarity. Which way is positive and which is negative. Matters for diodes, some relays, and every device power connection.
Positive trigger. A signal that switches to 12 volts to activate.
PTO. Power Take-Off. A shaft or hydraulic output from the transmission that runs equipment like a dump bed or a bucket. PTO engaged is a common auxiliary input.
Pull-up / pull-down resistor. A resistor that holds an input at a known high or low state so it doesn't float. See the Resistors chapter.
Relay. An electrically operated switch. A small current on the coil switches a large current on the contacts. See the Relays chapter.
Resistance. Opposition to current flow, measured in ohms.
Resistor. A component with a fixed resistance. See the Resistors chapter.
RPM. Engine revolutions per minute. Read from the bus.
Run. The key position where the vehicle is on and running. Ignition wire shows 12 volts here.
Short circuit. An unintended path, usually to ground, that lets current bypass the load. Blows the fuse if the circuit is fused correctly.
SIM. Subscriber Identity Module. The cellular card inside the tracker. Some devices have it soldered in; some use a removable card.
Solenoid. An electromagnet that moves a plunger. Door lock actuators and starter solenoids are examples.
Speed signal (VSS). The vehicle speed sensor wire. Older devices tapped it; modern devices read speed from the bus or GPS.
SPDT. Single Pole Double Throw. The five-pin relay with 30, 85, 86, 87, and 87a.
SPN. Suspect Parameter Number. The first half of a heavy-truck fault code. See the Codes chapter.
SPST. Single Pole Single Throw. The four-pin relay with no 87a.
Starter interrupt. A relay in the starter circuit that the tracker can open to prevent the vehicle from cranking. Also called starter kill or immobilizer.
Telematics. The combination of GPS, cellular data, and vehicle data that lets a fleet see where its vehicles are and how they're being driven. What we install.
Terminating resistor. The 120 ohm resistor at each end of a CAN bus. The vehicle already has two. Never add one.
Test light. See LED probe and see the Tools chapter on why the old incandescent type is not used.
Tolerance. How far a resistor's real value may vary from its stated value, as a percentage.
Trigger. Any signal that tells a device something happened.
Twisted pair. Two wires twisted together so noise cancels. CAN High and CAN Low are a twisted pair.
VIN. Vehicle Identification Number. The 17-character ID on the dash plate and door jamb. Most bus-connected trackers read it automatically; the platform uses it to identify the vehicle.
Volt (V). The unit of electrical pressure. A vehicle at rest reads about 12.6 volts; running, 13.5 to 14.8.
Voltage drop. The loss of voltage across a length of wire or a bad connection. A long, thin ground wire has a voltage drop, which is why grounds are short.
Watt (W). The unit of power. Volts x Amps.
Wire gauge. See AWG.
Y-cable. A harness that plugs into the OBD-II or J1939 port and provides two connections: one for the tracker and one that keeps the factory port available for a scan tool.
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This information is provided as a guide. Verify every circuit with a digital multimeter before connecting to it. Proper installation is the responsibility of the installer.
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