After connecting the wires make sure to test the voltage on the plug before inserting to the laptop or you might risk damaging your laptop.
White wire black wire blue wire laptop charger.
Set the meter to read voltage.
Turn the charger on.
Well the white is the sense and that will make laptop know that the right charger is connected the open sheild cable is the power when the big thick sheild is ground but you cant use 2 wire power instead you can use any other 3 wire board useing the same config in other power the sense can be blue like hp or red or grey its simple if you have a multimeter.
The black wire will be your hot wire and your whites are neutral depending on your switch setup you can wire nut the blacks together with an extra piece of wire coming from the wire nut to connect the hot to the light as well as the same method with your white wires.
Turn the meter on.
So i connected the white wire to the shilding wire and red wire to the core wire of the old 90w adapter s plug.
Carefully touch the meter probes black to the black wire red to the b w wire.
The second adapter however has three wires going out.
Recognize that the black wire is the positive one the white wire is the negative one and the green wire is the ground.
If the display shows a negative number black is positive b w is negative.
If the display shows a positive number black is negative b w is positive.
While powered the charger found red wire 19vdc white wire 0vdc black wire in the center pin for feedback to the board.
In another forum someone identified the sensor wire and left it out in the connection.
Identify the black positive wire on a ceiling light fixture.
If this is in reference to the many dell machines using the 3 pole 7 4mm barrel connector the 3rd wire goes to a 1 wire serial chip that the laptop reads to find out which wattage power adapter it is connected to so that it can limit its power dra.
I have read that an extra wire is used as some kind of a sensor.
White black blue for communication validate adapter and battery power it is best you use a multimeter to check.