Unless its a wideband A/F ratio gauge, dont waste your time. Widebands are very accurate and are used for tuning, the cheaper narrowbands are just fancy light shows.
Get a mechanical boost gauge and tap the vaccum line into where the stock boost gauge is at. The boost sensor is on the drivers side fender well. Thats where Im gettin my vaccum source from, works like a champ, the stock gauge still works too, its kinda cool. I like to spool the turbo up to 21 psi and watch the stock gauge peg out, its awesome.