Mine plugged in right under the steering wheel - the same place a mechanic would plug in a gauge to read trouble codes. It comes with two plug-in adapters.
I find it very useful in the mountains, especially when it's hot out. It allows you watch your transmission, water, oil, air intake, etc temps exactly.
The only thing that I think is hokey on it is when it tells me I'm getting 30 - 40 MPG in a 40' DP!!! But the fuel usage gauge is useful to remind you to get your foot out of it when there's no need for it.
I think it's the best thing going considering it only costs $149.
You can go to their web site and download the user's manual to see all of the functions and how it works.
Bill