ASE A6 lighting systems practice questions.

Five free practice questions on lighting systems: content area D of the ASE A6 Electrical/Electronic Systems test, 6 of its 50 scored questions (12%). They are in the ASE format: four options, one best answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Recall · Lighting Systems Diagnosis and Repair

   Why should a technician avoid touching the glass of a new halogen headlamp bulb with bare fingers?

   1. Skin oil left on the glass causes a hot spot that shortens bulb life
   2. Skin oil left on the glass bends the light and throws off the aim
   3. Static from the hand can discharge through the glass to the filament
   4. Skin oil reacts with the halogen gas and darkens the inside of the bulb
   Show the answer

   A. Correct. A halogen bulb's quartz envelope runs very hot, and oil from skin makes a spot that heats unevenly and weakens the glass, which can lead to early failure or a cracked bulb. Handle the bulb by its base, and clean the glass as the bulb maker directs if it is touched.

   Why not the others

   B. Aim is set by the headlamp housing and its adjusters, and a film on the bulb does not move the beam pattern. The real concern with skin oil is heat: it makes a hot spot on the quartz that shortens bulb life.

   C. Static is not what harms a halogen bulb handled bare-handed; the filament is sealed inside the glass. The damage comes from skin oil, which makes a hot spot on the quartz and shortens bulb life.

   D. The halogen gas is sealed inside the envelope and never touches oil on the outside, so no reaction takes place. Oil on the outside matters because it makes a hot spot that weakens the quartz and shortens bulb life.

2. Tech ab · Lighting Systems Diagnosis and Repair

   A technician is preparing to check headlamp aim with an aiming screen on a level floor. Technician A says the tires are first inflated to the pressures on the vehicle's placard. Technician B says the front and rear of the vehicle are bounced first to settle the suspension. Who is right?

   1. A only
   2. B only
   3. Both A and B
   4. Neither A nor B
   Show the answer

   C. Correct. Technician A is right: tire pressure sets how high and how level the vehicle sits, so the tires go to the placard pressures before aiming. Technician B is right: bouncing the front and rear settles the suspension at its normal height. The manufacturer's procedure also states the load, such as the fuel level, to aim with.

   Why not the others

   A. Not A only. Technician A is right: tire pressure changes ride height, so the tires are set to the placard pressures before aiming. Technician B is right as well: bouncing the vehicle lets the suspension settle at its normal height so a bind does not throw off the measured beam position.

   B. Not B only. Technician B is right that the suspension is settled by bouncing the vehicle before the aim is checked. Technician A is right too: low or uneven tire pressure changes the vehicle's height and tilt, so the tires are set to the placard pressures first.

   D. Both technicians are right. Technician A's placard tire pressures and Technician B's settling of the suspension both put the vehicle at its normal ride height and attitude, which the aim check depends on.

3. Recall · Lighting Systems Diagnosis and Repair

   After cleaning light corrosion from a taillamp bulb socket, which of these is applied to keep moisture away from the socket's terminals?

   1. Insulating spray varnish
   2. Copper-filled anti-seize compound
   3. Acid-cure RTV silicone sealant
   4. Dielectric silicone grease
   Show the answer

   D. Correct. Dielectric grease is a nonconductive silicone grease that seals out moisture and air; the bulb's contacts push through the film to meet the terminals, while the film keeps new corrosion from forming. A thin coat is enough.

   Why not the others

   A. An insulating varnish coats the contact surfaces themselves, so the bulb's contacts could not make a good connection. Dielectric grease seals out moisture while the contacts still push through it to meet.

   B. Copper-filled anti-seize conducts electricity, so a film of it can bridge the terminals of a dual-filament socket or leak current between them; it is made for threads. Dielectric grease seals out moisture without conducting.

   C. Acid-cure RTV gives off acetic acid as it cures, which attacks copper terminals, and once cured it can keep the bulb from seating and making contact. A thin coat of dielectric grease is what seals out moisture.

4. Recall · Lighting Systems Diagnosis and Repair

   In a thermal turn signal flasher, what opens and closes the contacts that flash the lamps?

   1. A magnetic coil that pulls the contacts open at high current
   2. A solid-state timer that switches a transistor on and off
   3. A relay coil pulsed by the turn signal switch contacts
   4. A bimetal strip that bends as lamp current heats it
   Show the answer

   D. Correct. Lamp current heats a bimetal strip made of two bonded metals that expand at different rates, so the strip bends and opens the contacts, then cools and closes them again. Because the heating depends on current, a thermal flasher's rate depends on the lamp load.

   Why not the others

   A. A thermal flasher has no magnetic coil doing the timing; heat is what moves its contacts. Lamp current heats a bimetal strip, which bends to open the contacts and returns as it cools.

   B. That describes an electronic flasher, which times the flashes with a circuit rather than with heat. A thermal flasher uses a bimetal strip that bends as lamp current heats it and straightens as it cools.

   C. The turn signal switch only selects which side's lamps receive the flasher's output; it does not pulse anything. In a thermal flasher the timing comes from a bimetal strip heated by lamp current.

5. Recall · Lighting Systems Diagnosis and Repair

   Many body control modules dim interior LED lamps without a rheostat. How does the module lower the brightness?

   1. It switches off some of the LEDs in each lamp
   2. It routes the lamp current through a series resistor
   3. It switches the feed rapidly and shortens the on-time
   4. It lowers the steady voltage it supplies to the lamps
   Show the answer

   C. Correct. This is pulse-width modulation: the module switches the lamp circuit faster than the eye can follow, and the shorter the on-time in each cycle, the dimmer the lamp looks. A lab scope shows the changing duty cycle, while a DMM on DC volts shows only an average.

   Why not the others

   A. Switching off LEDs would leave dark spots rather than an even, dimmer glow. The module keeps every LED in use and dims them by pulse-width modulation, switching the feed rapidly and shortening the on-time.

   B. A series resistor wastes power as heat and is the older rheostat method. A module dims LEDs by pulse-width modulation, switching the feed on and off rapidly and shortening the on-time.

   D. The module's lamp driver works as a switch rather than holding a steady lower voltage. It dims by switching the feed on and off rapidly with a shorter on-time; a lab scope on the output shows a square wave whose on-time changes as the dimmer moves.

02Answer key

03What area D covers

This content area covers lighting inside and outside the vehicle: headlamps of the halogen, HID and LED types, aiming and automatic leveling, fog and auxiliary lamps, stop, tail and license lamps, turn signals and hazard flashers, courtesy and dome lamps and their dimming, and trailer wiring along with electric trailer brake controllers.

The ASE test specification calls this content area “Lighting Systems Diagnosis and Repair”. It carries 6 of the 50 scored questions, 12% of the test.

• Diagnose dim, bright, intermittent or dead exterior lamps
• Replace, aim and level headlamps and fog lamps
• Test switches, relays, bulbs, LEDs and sockets
• Diagnose turn signal and hazard flasher faults
• Repair interior lamp circuits, dimming and controls
• Service trailer wiring, connectors and brake controllers

04What the questions turn on

Flash rate follows lamp current

A current-sensing flasher flashes fast when it sees less current than normal. One open bulb on a side does that, and so do LED bulbs, which draw far less than filament bulbs. A load resistor or a load-independent flasher cures the LED case.

Poor grounds light the wrong lamps

When a socket's ground is poor, current from one filament can reach ground backward through another filament and the other lamps on that circuit. Lamps then glow dim or light when they should be off, and the fault is the socket ground.

LEDs care about polarity

An LED lights only with current in one direction, so a wedge-base LED fitted the wrong way around stays dark where the old bulb worked. An LED also glows on a tiny leakage current that never lit a filament bulb.

Find what both sides share

When both low beams dim together, or both turn signals quit while the hazards still work, the fault is in something the lamps share: a feed, a ground, a fuse or a flasher. One open bulb affects only its own side.

05The other content areas

The A6 test has five content areas. Each has its own page of free questions:

The ASE A6 Electrical/Electronic Systems practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.

ToolboxPrep is an independent study site. It is not affiliated with or endorsed by ASE (the National Institute for Automotive Service Excellence). Our questions are original practice questions written to the published ASE test specifications; they are not actual test questions.