Help for Logic Probe & Pulser use at home

[Arichi Kushi]

So I need to check the wiring to my circuit board with the r.s.r logic probe and pulser... Can't go above 5v or I will mess up the chips. I was told about a truck I can do to test the levels at home... Get a 5v wall charger and cut it to expose the wires and connect them the probe.. But I have to wire to right to not mess up the board or not cause a fire lol....
I cut open a old charger that read Input: 100-240VAC output: 5vDC .. And I don't know which side is the negative or positive side..... I only know u connect red to red and black to black... But the wires inside are brown... Not red and black..... Any pointers??

 

[pinout]

You really need a simple voltmeter for this.

But.... if you are careful, look up an LED pinout for the positive and negative pins (usually determined by lead length) and the choose a series resistor to limit the LED current (typ 20mA and Vled at 1.5V so R approx 3.5/20 (kohms) = 180ohms, I would use around 270 to 330R). You then have an LED polarity tester....

One tip is cut your wires at different lengths, so they have less chance of shorting to each other and then tape up.

Be very careful with anything exposed that could be at the supply potential lethal as well as fire risk!