Issue with Zprobe and arduino shield

[techninja80]

So I picked up one of those red protoneer arduino shields, and uploaded Grbl 1.1 on the arduino. I have attempted to try the Z probe by putting the wire on scl, and one, and ground and tried to trigger it manually by just touching the wires together, but it does not trigger.  As I understand it should be just looking for a change I would assume to ground. But when I probe the scl pin its low on volts.  Is anyone familiar with how to do this.. Every thing I see on the internet says this should work. but its not for me. So I know my dumbass is doing something wrong.

[Kean]

From memory I've only used probing with grbl running on a Mega with my own custom shields.  I think I have a Protoneer shield here somewhere but not used it.
There should be an internal pullup enabled on the probe pin which by default is A5 on ATmega328.
Are you using a G38.x command to start the probing move?
Check you don't have inverted probe configured via $6, or that you uncommented DISABLE_PROBE_PIN_PULL_UP in config.h.