A dc terminal polarity tester for use in repairing automotive electrical systems. It is a shirt-pocket sized pen shaped tester, having a probe at one end and a visible bi-color light-emitting diode (LED) at the other end. The tester is provided with a long power lead that includes clips or a connector to connect to a 12 volt dc source. When the tester is connected to a power source, such as an auto battery, the tester probe tip may be touched to a terminal for a polarity check. If the terminal is positive (+), the LED will emit red light. If negative (-), the LED will emit green light. The device may include a buzzer. If so, a positive probed terminal will activate the buzzer in addition to lighting the LED red. The tester is small in size and inexpensive.