If I understand your question, you don't have the trip computer. It
can't be easily added. You'd need to get a whole new cluster for
starters (the trip display is not separate), and a new wiper stalk
with the control switches. I'm not even sure if all the wiring is
there (I haven't looked at a non-trip A4 yet to see), but my guess
is the harnesses are probably the same (just like other options in
the car which have wiring even if you don't have the option).

Curt