You don’t even need any special tools or parts, all you need are:
1. A 9V Battery
2. Black Electrical Tape
3. 2 pieces of 18-22g wire (color coded)
4. Wire Strippers
This simple DIY only takes a few minutes of your time and will be able to save you hours of headache in the future!
Gather your materials together. Make sure to only use this 9V battery, never use any battery exceeds 12V which can potentially damage the LED. Using a battery less than 9V may not allow the lights to even turn on.
Strip some plastic sheathing off of both ends of the wires and hook the wires to the battery's positive and negative. (Make sure to hook the red wire and black wires to the battery positive and negative terminals, respectively).
Use the black electrical tape to cover the positive and negative terminals up.
Now you have made your own LED tester. You can connect the red and black wires to the LED bulb to check which side of the LED bulb is positive and also to see whether a LED bulb is defective (NOTE: If an LED bulb does not light up at the first time, please flip the two wires around and try again)