How do I use the ground isolation jumper?

How do I use the ground isolation jumper?

Just set the jumper by ear. For most systems, the ISO (isolated) position is the best option. This provides full ground loop isolation between the signal and power grounds. Only try changing this if you hear engine noise from your stereo. You can move this jumper setting while the system is operating and the car's engine is running to see if another position works better. Choose the setting with the least engine noise.