I would not touch the gauges, its not uncommon for them to be temperamental and given the electronic control module for the dash and lights who knows if anything extra in the circuit might cause issues?
There may be a spare pin location that becomes live in the ignition switch multi connector or you could tap into the wiper feed. As mentioned above the radio is another but remember most modern radios have 2 input feeds, I permanent live and one ignition switched so a few moments with a test lamp should show which is which.
