Abstract: This specification discloses a vehicle electrical system tester which connects in parallel across the vehicle battery and the portion of the electrical system to be tested and measures voltages upon selective actuation of portions of the vehicle electrical system as determined by individual characteristics of a particular vehicle electrical system. Comparison of these measured voltages with predetermined values is used in evaluating whether the electrical system is operating properly. The vehicle electrical system tester and a memory are packaged in a portable measuring unit which is periodically coupled to an analyzer for analyzing measured voltage data and updating instructions for the portable measuring unit. The analyzer can determine a pattern of recurring faults and provide information to correct the manufacturing process to remove the faults.

Abstract: This specification discloses a vehicle electrical system tester which connects in parallel across the vehicle battery and the portion of the electrical system to be tested and measures voltage changes upon selective actuation of portions of the vehicle electrical system. Comparison of these measured voltages with predetermined values is used in evaluating whether the electrical system is operating properly. The method of testing using the apparatus includes measuring a first voltage level after connection of the apparatus, actuating a portion of the vehicle electrical system, measuring a second voltage level, calculating a voltage difference as a function of the first and second voltage levels, comparing the voltage difference to a predetermined voltage magnitude, and determining if the actuated portion of the electrical system is operating properly. Additional sensitivity can be achieved by establishing a third voltage level through the use of a calibration resistor.

Abstract: This specification discloses a connector plug for connecting a vehicle electrical system tester to the cigar lighter socket of a vehicle for the purpose of testing portions of the vehicle electrical system. The connector plug can have two separate connections to the positive side of the battery so that one connection can be used to power the tester and, independently, the other connector can be used to monitor the voltage change across the battery. Further, the plug can also include a static shield for eliminating a static electric charge on the vehicle electrical system tester as the plug is inserted into the cigar lighter thus preventing the static charge from damaging sensitive measurement circuitry or altering memory circuitry.