Well i hooked up the m300 and connected the power wire to the power wire on the ecu and the ground to the ground wire on the ecu. also i have the battery in the trunk. so i go switch the batter to the on postion and the plx turns on even when the key isnt in the ignition. is that normal? it just displays " air". did i hook up the power wrong or something?

 

yea, you hooked it up to the constant 12V not the switched.

 

which pin in the 12v switch?

 

not sure, but you can check it with a voltmeter.