We presume you mean a ScanGauge II....
If you can get it (with the lead and instructions) cheap on eBay then get it....obviously.
As to where you fit it depends on what audio headunit you have.
If you have a Radio5....
then the ScanGauge II will fit perfectly in the cubby hole underneath it.
You can either have the lead out the driverside end and then across and down and into the
gap round the steering wheel side panel (as I have/had).
Or.....
if you're not fussy...have the lead out of the back of he ScanGauge II...and make a small hole
in the rear of the cubby hole and feed the lead thru there and route it round to the OBD2 port
that is to the left and under the steering wheel panel.
If you have a Radio6 or any other double DIN headunit....
Not much choice as there's no cubby hole space under it........
Which just leaves 2 choices.
firstly the space on the dash to the right of the steering wheel......
I'd advise sticking one piece of velcro to the the back of the ScanGauge II and the other matching
piece of velcro stick to the dashboard.
(loosely placed in this picture..the cable should be under it and the gauge up and back to the panel)
Or......
secondly, use a similar method of fitting and place it to the right side of the shelf on the passenger side...
in other words right next to the head unit, but to avoid having the lead trailing across the lower dash
you would have to make a hole in the corner of the shelf to run the lead thru ! (No picture for this)
