Electricity
A 90 W device runs on 12 V. What is its expected current draw?
7.5 A
What is the primary purpose of a relay?
Low current control circuit to switch a higher current load
What protects wire through a sheet-metal hole?
Rubber grommet
Name the first two checks in the course lightbar diagnostic order
Battery Voltage, then fuse
What does a speaker convert?
Electrical signal to sound
What is the main function of an antenna?
Transmit and receive RF energy
State Kirchhoff's Law in plain language
Current entering a node equals current leaving it
When would you use a high-current switch?
When directly powering a small accessory
What happens if a wire is undersized?
Excessive voltage drop and overheating
What does a 1.4 V battery-to-device difference suggest?
Possible excessive voltage drop; test power and ground under load
What hazard can remain after strobe power is disconnected?
Stored high voltage
What is the recommended antenna orientation?
Level and unobstructed
What is the difference between voltage and current?
Voltage is the electrical pressure pushing electrons (volts); current is the flow of charge (amps)
Which switch type is a simple ON/OFF control?
SPST
What two clearances are taught for moving parts and exhaust?
3 inches from moving parts; 6 inches from exhaust
A recorder has power but no audio. What setting should be checked?
Volume control
What is the function and purpose of a wig-wag circuit in an emergency vehicle?
Alternately flashing headlights, meant to increase visibility and provide a warning to other drivers
What is RFI?
Unwanted radio-frequency signal disruption/interference
How can fuses help isolate a parasitic draw?
Remove one at a time and watch for a drop measured in current
Why use a relay to control a high-load device?
A small current can control a larger current and protect its switch
Why put a fuse near the power source?
To protect as much of the wire as possible
A device fails when going over bumps in the road, what is the likely cause?
Loose connection, damaged wire or poor ground
What is the purpose of a shutdown delay timer?
Shut off selected loads after delay/low voltage to protect the battery and equipment
Why must an optical pre-emption emitter have a clear path?
Optical systems require line-of-sight
Why should you avoid probing unknown SRS wires with a test light?
It may trigger the supplemental restraint system
A relay clicks, but the device doesn't work. What are you next checks
Contact supply, switched output, device voltage and ground
Why is an oversized fuse dangerous?
It may fail to protect wiring, allowing overheating/fire risk
Why test voltage under load?
Resistance may cause voltage to collapse when current flows
Give two causes of weak siren output from the course
Voltage drop, incorrect speaker impedance, or failing amplifier
Name two push-bumper considerations from the guide
Airbag deployment interaction and added weight/handling