A circuit tester for both 14-volt and 42-volt automotive electrical systemsincludes a housing with a probe tip at one end and a ground connector at theother end. A battery-powered voltage detection circuit in the housing includesa plurality of comparators, each having one input connected to an input signalfrom the probe tip and a reference input connected to a tap of a tappedvoltage divider providing plural reference signals having amplitudesrespectively corresponding to industry-standard voltage levels, thecomparators being arranged in two groups respectively corresponding to 14-voltand 42-volt automotive systems. Series-connected LEDs have their cathodesrespectively connected to the outputs of the comparators, and are arranged forrespectively being viewed through apertures in the housing arranged in twoseparate rows. The interconnections are such that only one LED at a time isilluminated, i.e., the one corresponding to the highest reference signal levelwhich is equaled or exceeded by the input signal.
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