Does the PA-44's squat switch disable the stall warning? I've read the AFM and looked online about the gear system for the PA-44 Seminole and there is apparently a squat switch on the right main gear that disables the stall warning whilst on the ground. However during my pre-flight I have tested the stall warning with the battery master and avionics master on and it worked.

Is the stall warning squat switch not a feature on the newer PA-44s any more? The one I train in is about a year old now.
Are you sure you're talking about the stall warning? I believe you're talking about the horn that activates when in the landing configuration with no gear down(e.g throttle retarded, flaps down). 

The 44 has 2 electric stall warning tabs that won't be actuated on the ground.