Five ASE T6 Electrical/Electronic Systems practice test questions, answers included.

1. Recall · General Electrical/Electronic System Diagnosis

   A truck's marker lamp circuit uses the wire size the manufacturer specifies for its 15-amp fuse, and the fuse has blown twice. Why is a 25-amp fuse never fitted in its place to stop the blowing?

   1. The larger fuse would raise the current to the lamps
   2. The wire could overheat before the fuse opened
   3. The larger fuse would add resistance and dim the lamps
   4. The fuse protects the lamp bulbs, not the wiring
   Show the answer

   B. Correct. A fuse is sized to protect the wire it feeds: it must open before the current reaches a level that overheats the wire and its insulation. A 25-amp fuse on wire sized for 15 amps lets an overload or partial short heat the harness, so a fuse that keeps blowing calls for finding the short or overload.

   Why not the others

   A. A fuse does not set the current; the voltage and the circuit's resistance do. The larger fuse simply lets more current flow before it opens, and that is the danger to the wire.

   C. A higher-rated fuse has a heavier element with less resistance, not more, so it would not dim the lamps. The concern is that it would not open before the wire overheated.

   D. Circuit protection is sized for the wiring; a bulb draws only what its own resistance allows. The fuse's job is to open before the wire overheats, which a 25-amp fuse on this wire might not do.

   ID T6-A-002 · Task T6-A-6 (ASE task list)

2. Recall · Battery and Starting System Diagnosis and Repair

   What does the over-crank protection thermostat in a heavy-duty starter motor do?

   1. It limits how much current the motor draws on a cold engine
   2. It opens the starter control circuit if the motor overheats
   3. It keeps the pinion from engaging while the engine is running
   4. It cuts battery current if the starter cable shorts to ground
   Show the answer

   B. Correct. Long cranking heats the armature and fields quickly, and the thermostat inside the motor opens the control circuit to the magnetic switch when the motor gets too hot. It closes again once the motor cools, so the starter can be used after a cool-down instead of burning out.

   Why not the others

   A. The thermostat does not regulate current; starter draw rises with engine drag on a cold engine. The thermostat responds to motor temperature and opens the control circuit when the motor overheats from long cranking.

   C. Blocking the starter with the engine running is done by a crank lockout, usually in the engine control module. The over-crank thermostat senses motor heat and opens the control circuit when the motor overheats.

   D. A shorted cable is protected against by fusible links or circuit protection in the feed, not by a thermostat in the motor. The over-crank thermostat opens the control circuit when the motor overheats from long cranking.

   ID T6-B-002 · Task T6-B-10 (ASE task list)

3. Recall · Charging System Diagnosis and Repair

   A trailer's liftgate battery is charged from the tractor through a 6 AWG feed wire and a 6 AWG ground return, each 60 ft long and rated 0.40 ohm per 1,000 ft. The tractor end holds 14.0 volts, and the liftgate battery is taking 30 amps. What voltage reaches the liftgate battery?

   1. 12.56 volts
   2. 13.28 volts
   3. 13.64 volts
   4. 14.00 volts
   Show the answer

   A. Correct. The current flows out on the feed and back on the return, so 120 ft of wire is in series: 120 x 0.40 / 1,000 = 0.048 ohm, and 30 A x 0.048 ohm = 1.44 volts lost. 14.0 - 1.44 = 12.56 volts, which is why long trailer charge circuits need heavy wire and good connections.

   Why not the others

   B. This counts only the 60 ft feed wire (0.024 ohm x 30 A = 0.72 volt). The return carries the same current through another 60 ft, so the loss is 1.44 volts and the battery gets 12.56 volts.

   C. This treats the feed and return as parallel paths (0.012 ohm x 30 A = 0.36 volt). They are in series, one after the other, so the resistance is 0.048 ohm and the battery gets 12.56 volts.

   D. Wire resistance drops voltage whenever current flows, so the battery cannot see the full 14.0 volts while taking 30 amps. The 120 ft of wire loses 1.44 volts, leaving 12.56 volts.

   ID T6-C-020 · Task T6-C-5 (ASE task list)

4. Recall · Lighting Systems Diagnosis and Repair

   A sleeper's bunk lamp can be switched from the door or from the bunk by two single-pole, double-throw switches joined by two traveler wires. If one traveler wire breaks open, how will the lamp behave?

   1. It lights at reduced brightness from either of the switches
   2. Either switch still turns it on and off in every position
   3. Only the switch at the bunk can still turn it on and off
   4. Either switch works only with the other in one position
   Show the answer

   D. Correct. The lamp lights only when both switches select the same traveler, so with one traveler open it can light only through the good one. Whichever switch sits on the broken traveler holds the lamp off, and the other switch does nothing until the first is moved to the good traveler.

   Why not the others

   A. An open traveler breaks the path completely in the positions that use it; it adds no resistance in the positions that use the good traveler, so the lamp is either fully on or off.

   B. Normal operation needs both travelers, because the lamp is lit through one or the other depending on the two switch positions. With one open, every combination that uses the broken traveler leaves the lamp off.

   C. The circuit is symmetrical: the broken traveler affects both switches the same way, so neither one is favored. Each switch can work the lamp only while the other sits on the good traveler.

   ID T6-D-014 · Task T6-D-6 (ASE task list)

5. Recall · Related Vehicle Systems Diagnosis and Repair

   A sleeper cab has a cigarette lighter socket and several 12-volt auxiliary power outlets that look the same. Why does the manufacturer warn against pushing a lighter element into an auxiliary power outlet?

   1. The outlet's center contact is the ground side
   2. Outlet voltage is too low to heat the element
   3. It may stay energized and overheat the socket
   4. The outlet would switch the element off too soon
   Show the answer

   C. Correct. A lighter socket has clips that hold the element in while it heats and then release it; a power outlet has no such release, so the element can stay energized, overheat the outlet and its wiring, and blow the fuse. Lighters go only in a socket built for them.

   Why not the others

   A. The center contact of a 12-volt outlet is the positive side and the shell is ground, just as in a lighter socket. The problem is that the outlet has no clips to release the hot element, so it can overheat.

   B. Both the lighter socket and the power outlets run on the truck's 12-volt system. The danger is the opposite of too little heat: with no release in the outlet, the element can stay on and overheat it.

   D. An outlet has no mechanism to switch a lighter off at all; that is the hazard. Without the release clips of a lighter socket, the element can stay energized and overheat the outlet.

   ID T6-E-009 · Task T6-E-13 (ASE task list)

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