How to Use an Automotive Test Light (Circuit Tester)

Here is a quick tutorial on how to use an automotive test light/ circuit tester to test for power. I am demonstrating with a Cornwell 6v/12v light

[chrispowell]

Thanks my fired, best video I've seen on these teaters.

[GHOST]

Sorry to be naive but red means positive?

[gamerdiydad]

Would this cause issues in PCMs. (I.e Connecting neg to pos)

[jennatrusty]

How do you know which fuses need the engine on for them to light up how do you know I also thought the car had to be turned off for you to check the fuses I thought that was the whole thing