the instrument panel does not contain any single wire for data.
the obdii connector has the data wire for the communication of a device to hook up and it goes to computer.
if you tie in at the main gauges harness you will have to use each wire(example speedo,temp., neutral light ect.)
if you use the one wire (plus pos and neg) whatever you hook up has to the capability of communicating
with the computer
you might have some one else come on to explain it better.