Help!

I have been trying to get my homebuilt probe working for some time without luck, I am sure I now have the wiring right but the probe routine doesn't work.  I have reverted to testing by using a key to simulate the probe tripping under inputs using emulation,  however I tried assigning P and when I press the P key the led does not light up?  Anyone have this problem? I have also tried other keys same problem?

Thanks

I use this all the time for testing and mine works fine. I have it assigned to the "/" key.

hmm ..tried this on a new machine and it works fine wonder if it's the computer giving me all the grief?