frequency of data wires in a vehicle?

So what kind of signals are you looking for????

Data wires are typically smaller then power wires.  I don't know exactly what you are trying to do, but there are "other" easier ways to tell if you have the correct wire.

The only time I've ever need an o'scope on a car is to actually decode the data being sent.

If your wire shows +12v DC constant or +12v DC switched, there's no data.  period.  They do not multiplex data on 12v DC wires.  Computer data systems on cars are based on 5v format.  Shove 12v DC onto a data wire and goodnight Irene.  So, if you test the wire and it' shows 12v DC, you are fine.  When the wire is multiplexed to control other features in the cars, such as Mopar lights and door locks, you'll see three different DC votages depending on what you are trying to control.

Bottom line is that you will not see +12V DC on a data wire.

Yeah, like I said if a wire has battery voltage on it constantly it can't have data on it.  Throw a volt meter on it and watch it for 30 or even 60 seconds - if it stays constant then you are good to go.   Another good rule of thumb is to never use any wire smaller then 18awg wire for power - that right there should eliminate your issue as most data wires are 20awg or smaller.

Also, if you just need switched and ignition I would always look for the steering column wires or the ECU power wires - in both cases the wires will be larger then most other wires in the area.