Yeah that is the correct procedure to test the light.
A fuse is always a good idea good job!
The red wire is positive terminal and the black wire is the negative (GND) terminal.
For the LEDs the polarity is important (LED = Light Emitting Diode) so basically an LED is a diode. And just like a diode it will conduct electricity one way and will be very high resistance (we can approximate it as infinite) the other way. There will be no damages to the LEDs if the polarity is reversed so you can test with confidence if one way doesn't work then just swap the wires (change the polarity) and it will lit.