Hello - I just purchased a new touch probe in which I have a question about the wiring. My existing touch probe is a home made 2-wire device and this one is  3-wire system NPN-NO type, red to power, blk to ground, and a yellow signal wire. I have my existing probe wired to input 4 on my motion control board and hence input 4 used in Mach3 and it works good however I am wanting a little better accuracy so that's why acquired this one. Where and what purpose is the signal wire used for and how to tie it in?

Here is a link to the probe which includes the wiring diagram.
https://www.lollette.com/3D-Touch-Probe

A link to the motion control board used in my system
https://buildyourcnc.com/item/electronicsAndMotors-electronic-component-breakout-Mach3-USB-Board

Hello, the wiring diagram on the probe website is unusually well commented. It shows a simplified version of the probe's output circuit. Not shown are the mechanical sensing switch or the LEDs but the text describes their action.
The diagram shows a 10K pull up resistor and a switch which represents the output of the NPN transistor. When the probe tip is displaced the transistor connects the yellow signal wire to ground. Electrically this is like the old probe tip touching a grounded metal part.

All connections are made to the interface board.
Black wire to the GND terminal
Red wire to the +5V terminal
Yellow wire to input 4 terminal (probe input)

Thanks for your response. That's was how I was intending to hook it up but needed someone with a little more electronics knowledge to confirm and explain it better. So the primary difference is my 2-wire homemade unit which is a "probe type" not a "touch plate" as I have both. The simple 2-wire method input 4 circuit opens when the probe is activated directly where as the 3-wire method is maybe a safer switching method by way of the transistor? I not an electronics guy, just trying to understand it a little better. As far as the motion control board don't the inputs share the same feed as the 24V supply.
When I switch back and forth between the probe and touch plate I have to change the "Active Low" in the config menu for the probe. With the probe being "Active Low" enabled and the touch plate vice versa. I assume the 3-Wire probe will be set to "Active Low" also, is this correct?

Randy

Hello.
・Do you want to use "3D Touch Probe edge finder" using the input terminal (No. 4) of "Mach3 USB CNC Interface"?
・I think the red, black, and yellow connection methods of your "Mach3 USB CNC Interface" are correct.
・ After that, if you want to check whether it is working properly or not, click the tab of Diagnotic (Alt 7), and if "Digitize" flashes, it's OK.

All connections are correct, it's working great!

It was good.
In the future, Mach4 will be more convenient.
Mach4 uses Touch and Probing properly.
In fact, I recently changed from Mach3 to Mach4.