✓ TradeExamPro

TradeExamPro › Automotive › Diesel and heavy truck

Electrical practice questions

21 questions from the diesel and heavy truck practice test.

Electrical practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Four 12-volt batteries rated 950 CCA each are connected in parallel. What is the battery bank's rating?

  1. 48 volts, 950 CCA
  2. 12 volts, 3,800 CCA
  3. 12 volts, 950 CCA
  4. 24 volts, 1,900 CCA
Show the answer

B. 12 volts, 3,800 CCA

Parallel connection keeps voltage at 12 volts and adds the cranking capacities: 4 x 950 = 3,800 CCA. The 48 volt answer would be all four in series.

Reference: ASE T6 Electrical/Electronic Systems task list, battery (series and parallel connection)

A 12-volt battery at about 70 degrees F is load tested at one half of its CCA rating for 15 seconds. What minimum voltage must it hold to pass?

  1. 9.6 volts
  2. 7.2 volts
  3. 11.8 volts
  4. 12.6 volts
Show the answer

A. 9.6 volts

A good battery stays at or above 9.6 volts under this load. The 12.6 volt figure is the open-circuit voltage of a fully charged battery with no load, which a battery under a heavy load test cannot hold.

Reference: ASE T6 Electrical/Electronic Systems task list, battery (load testing)

Four 21-watt marker lamps are wired in parallel on a 12-volt circuit. What is the total circuit current?

Answer in A.

Show the answer

7 A

Total power = 4 x 21 W = 84 W. I = P / E = 84 W / 12 V = 7 A.

Reference: ASE T6 Electrical/Electronic Systems task list, general electrical diagnosis (power formula)

Other topics