12-volt tester plus

The 721-probe tester has a light and a buzzer that sounds when 12 volts are present.  It can also detect if you have an AC or DC circuit, and if it is DC, it will indicate which leg of the tape run is positive.
There are two red LEDs: one behind each pin probe.  Push the two pins into the tape run: One pin into each copper run.  If 12 volts are present, one or both LEDs come on, and the buzzer will sound.  If one LED lights — you have 12 volts DC present, and the probe in front of the lighted LED is touching the positive lead.  If two LEDs are lit, you have 12 volts AC.  In both cases, the buzzer will sound, indicating that 12 volts are present.