Positive or negative interior lamp switching

[dfj7584]

I'm hooking an aftermarket alarm wire to the dome light and need to know if the system shows volts or ground with doors closed. Thanks!

 

[BrooklynBay]

Welcome to this forum! I see that you are new here. The best way to tell is by either looking at a wiring diagram, or using a test light with the alligator clip connected to the vehicle's body ground.