If you've ever been frustrated trying to track down a wiring problem, then you'll really appreciate that diagnostics are also integrated into the system. Throw any switch, and the Mastercell will give you confirmation on its LCD panel to isolate wiring problems. The Mastercell has a blinking LED light that tells you it is working properly and that its connections to the Powercells are functioning. In addition, the Powercell has an LED telling you which circuit has been turned on. If it's glowing brightly (or blinking if it's turn signal), everything is fine. If the LED is only glowing dimly, then you know that the issue is between the Powercell and whatever function you are trying to activate.