Free Law Enforcement Vehicle Installation Technician Practice Questions

Question 1

A light bar resets when its high-output warning pattern runs. During the fault, battery-post voltage holds at 13.8 V, the positive-feed voltage drop is 0.12 V, and the light bar's ground terminal measures 2.1 V above battery negative. Light-bar current is within its specified range just before the reset. Where do these readings direct the repair?

Accepted Answer

The light bar's ground-return path has excessive resistance.

Answer

The alternator cannot maintain charging voltage at the operating speed.

Answer

The light-bar controller is failing despite receiving a sound power supply.

Answer

The positive supply wire is losing excessive voltage between the battery and light bar.

Question 2

A computer mount clears the vehicle manufacturer's passenger-airbag deployment envelope when stowed but enters it when swung toward the passenger. The SRS warning lamp completes its normal check. An installer proposes adding a 'stow before driving' label. How should this installation be handled?

Accepted Answer

Change the mounting arrangement so every usable position clears the deployment envelope.

Answer

Accept it if the mounting base uses the equipment manufacturer's highest-strength hardware.

Answer

Accept it if the arm is stowed whenever someone occupies the front passenger seat.

Answer

Accept it after an SRS scan confirms that the installation introduced no fault codes.

Question 3

A control module switches an auxiliary relay through a low-side transistor. Relay terminal 86 receives positive 12 V, and terminal 85 connects to the transistor's switched ground. The module manufacturer requires an external flyback diode. Select the connection that suppresses coil turn-off voltage without shorting the supply when the relay is energized.

Accepted Answer

Across the coil, with the cathode at terminal 86 and the anode at terminal 85.

Answer

Across the coil, with the anode at terminal 86 and the cathode at terminal 85.

Answer

In series with the coil feed, with the anode toward positive 12 V and the cathode toward terminal 86.

Answer

Across the normally open load contacts, with the cathode toward the fused supply and the anode toward the accessory.

Question 4

A replacement 12-volt lead-acid starting battery is labeled 800 CCA. Which test performance does that rating represent?

Accepted Answer

Delivering 800 A for 30 seconds at 0°F while maintaining at least 7.2 V.

Answer

Delivering 800 A for 30 seconds at 32°F while maintaining at least 7.2 V.

Answer

Delivering 800 A for 30 seconds at 0°F while maintaining the full nominal 12.0 V.

Answer

Delivering a steady 25 A at 80°F until the battery's terminal voltage falls to 10.5 V.

Question 5

An alternator rated at 250 A has a verified continuous hot-idle output of 130 A. At hot idle, vehicle systems require 80 A, essential warning and communications equipment requires 35 A, and deferrable chargers require 30 A. The fleet requires at least 10 A of unused charging capacity in this condition. Which operating configuration satisfies that requirement without sacrificing essential equipment?

Accepted Answer

Shed the chargers at hot idle; the remaining loads leave 15 A available.

Answer

Keep every load powered; the alternator's 250 A rating leaves sufficient capacity for the installation.

Answer

Keep every load powered; use the battery to cover the deficit until engine speed increases.

Answer

Disable all auxiliary equipment at hot idle until a higher-output alternator has been installed.

Question 6

Two identical grille-mounted LED heads are meant to alternate left and right, but they flash together. Both use the same supported two-phase flash pattern, their synchronization connection tests good, and their supply voltage is stable. What adjustment will produce the intended alternating sequence?

Accepted Answer

Program opposite phase assignments while retaining the common flash pattern and synchronization.

Answer

Select a different flash-pattern number on one head while retaining the synchronization connection.

Answer

Disconnect the synchronization wire and energize one head slightly later than the other.

Answer

Replace both heads as a matched pair before returning the warning system to service.

Question 7

An auxiliary distribution stud is fed by a cable protected with a 60 A fuse. A recorder has separate main-power and ignition-sense inputs. Its main-power branch wire is too small to be protected by the 60 A fuse, and the equipment instructions call for a 5 A fuse. To protect the full main-power branch, the 5 A fuse belongs:

Accepted Answer

At the positive takeoff, before the smaller wire runs to the recorder.

Answer

At the recorder's positive connector, after the smaller wire has crossed the vehicle.

Answer

In the recorder's ground lead, next to the chassis connection.

Answer

In the ignition-sense lead, upstream of the recorder's timed-shutdown control input.

Question 8

A quarter-wave mobile antenna that requires a ground plane is fitted to a fiberglass roof panel. The coaxial cable and connectors test good, and the mount has DC continuity to the chassis, yet the installed antenna match is poor. What is missing from the installation?

Accepted Answer

A conductive ground plane at the feedpoint, sized for the antenna and operating frequency.

Answer

A longer wire from the mount to battery negative to provide a more direct DC return.

Answer

A coaxial feedline cut to an exact multiple of one-half wavelength to replace the missing roof metal.

Answer

A heavier coaxial connector shell to lower DC contact resistance between the mount and cable.

Question 9

A push bumper, prisoner partition, and fixed cargo equipment add 280 lb to a patrol SUV's scale weight. No change to its certified weight ratings has been authorized. Which statement belongs in the vehicle's payload handover notes?

Accepted Answer

GVWR is unchanged; the remaining allowance under that rating decreases by 280 lb.

Answer

GVWR rises by 280 lb; the original occupant and cargo allowance is unchanged.

Answer

GVWR falls by 280 lb, while the original allowance for occupants and removable cargo stays unchanged.

Answer

GVWR is unchanged; fitting heavier rear springs restores the 280 lb allowance for occupants and cargo.

Question 10

A radio develops a buzz only when a new LED light bar is on. To isolate the cause, a technician places a separate receiver on an insulating surface and powers it from its own battery. Its only external connection is the vehicle antenna cable; it uses its built-in speaker. The buzz is reproduced, then disappears when a matched 50-ohm termination replaces the antenna cable at the receiver. Which interference path do these tests identify?

Accepted Answer

RF interference entering through the antenna or its feedline.

Answer

Conducted interference entering through the vehicle's radio power lead.

Answer

Audio interference entering through the vehicle's external-speaker wiring.

Answer

A failure inside the original radio that requires replacement of that radio.

Free Law Enforcement Vehicle Installation Technician Practice Questions

Domain 1: Definition and Terms

Question 1

Question 2

Domain 2: Installation

Question 3

Question 4

Question 5

Domain 3: Basic Electrical

Question 6

Question 7

Domain 4: Troubleshooting and Repair of Auxiliary Equipment

Question 8

Question 9

Question 10

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