I assume you (like everyone else) is mounting the boost gauge on the a-pillar.
Mine was there when I bought it, but I did mount the two gauges in the console pocket under the radio for Oil & Water. When doing so, I found a wire up above the pocket that lit the pocket up when the head lights were turned on. So, I removed the bulb (since tray is now covered up), and spliced into the line.
I'm thinking you can feed a wire to it.
HTH.