door pin polarity

I've been searching for quite some time on this and haven't been able to figure out anything. I have a 84 buick regal which it's said has a negative pin switch. I got a dmm & a polarity test light. both of which when I connect the ground lead to a ground and tap the white wire at the pin switch says it's +12 v(dmm) and red light(test lights positive polarity) so it's safe to assume it's actually a +12v from those but EVERYthing ive read says if it's not ford it has -. even the alarmtek install guide I have says that. I'm uncertain as to what it really is. I would prefer not to have someone just say its this and go with that. I would like to know how to prove it's one or the other. since the pin switch screws into the body that tells me it's negative also but the tools say otherwise. what makes a circuit a - or a +? I've even connected a light bulb from the white wire to a ground & it lights up, meaning positive right. But, if it's a positive wire then why doesn't it short circuit being touched to the body(cause its negative right? but if it's negative why did the light bulb light up) I'm really confused on this. which is annoying since I do get into electronics a little bit so I should be able to understand this but I cant seem to be able to. so, any help?

A negative trigger door switch will read twelve volts positive on a dmm when all the pins in the circuit are depressed! The voltage applied is relatively low, but it would suffice to illuminate an led such as that of your test light!commit your way to jehovah and he will act in your behalf. psalms 37:5

its a two door car & the passenger side door closed the pin removed from the door jam if i have the pin pushed in(breaking the circuit) or not the reading is the same on both the dmm & the test light

cant edit posts...the pin on the drivers side removed the pin on the passenger side is still in place in the door jam

The bulbs actually do work when the switch isn't mounted. on my pin switch I have 2 wires going to it. One is the wire wire the other is a kind of flesh colored wire. when the switch is pressed the 2 wires are disconnected breaking the circuit. But yeah, when I mounted the switch & read the white wire I got +12v when the door is closed & null with it open as T&T tech said. I understand your explanation on how the negative polarity works. Thank you so much on explaining how that works for me. Both of you have been very helpful. Now, back to the install job.