The PT-9A+ has a safe, low voltage output pulse that means no damage to CAN Bus wires, Air Bag wires or other sensitive circuits if you mistake other vehicle wiring for audio signal or speaker wiring. 
No more popping speakers with power tool batteries, please! If you do any kind of audio system installation, particularly OEM audio integration, the PT-9A+ is a tool you can’t be without.
 
Features:
Built-In Selectable Pulse Generator - Preamp Level (RCA) and Speaker Level Jacks
Built-In Compact Microphone for Testing/Verifying Acoustic Speaker Polarity
Speaker Level Jacks can be configured as Inputs for Electrical Signal Polarity Testing
Low Volume Threshold for Safe Testing – System volume does need not be loud to test
Easy-to-Understand Polarity LEDs – Green = Correct, Red = Incorrect
Includes USB Thumb Drive with Polarity Pulses and Pink Noise
Comes with a Protective Storage Case, Quick Start Guide and Insulated Test Leads
 
Applications:
Test polarity of audio system speakers before starting an installation or tuning
Generate pulses into the audio system to verify speaker location and polarity
Test polarity of OEM audio signals at the source unit or amplifier output (up to 4V)
Identify speaker location and polarity in OEM audio systems using internal pulse generator
Verify polarity shift in active or passive crossovers (especially 12dB/octave applications)
Optimize subwoofer polarity to blend with other system speakers for “up front” bass