rear

So I'm about to do a rear differental fluid service, I have a 2000 gmc jimmy slt 4x4 4 door, and I cant find out what gear ring size I have. It's either 7.xx or an 8.xx. It determines the gasket I'm trying to replace and I don't want to buy the wrong cover and gasket. So my question is if...

I have a 2012 Denali and have purchased a mirror tap for my radar detector. I need to know which wire is the 12 volt and which is the ground. I have the nav system, so the mirror does not have the rearview camera in it. Thanks.