This tester can be used to check the polarity of any power source, and is therefore very useful when installing automotive equipment, alarm systems or anything else you can think of. Because this circuit is so simple and cheap, even frying one with an over voltage is not a big deal.
Part Total Qty. Description Substitutions
R1 1 1K 1/4W Resistor
D1 1 Green LED
D2 1 Red LED
D4, D5, D6, D7 4 1N4001 Silicon Diode 1N4004, 1N4005, 1N4007
MISC 1 Board, Wire, Case, Probes
Visit Here for more.