well i got egt boost oil and water and i had one more hole to fill so i just got the a.f and i am starting to install them i know how to do all but the a/f i dont know what wire to splice into
You are going to need a wideband o2 sensor in order for that gauge to work properly. I would NOT recommend splicing that into the factory o2.
Yeah, I agree that an a/f gauge on a stock o2 sensor is a waste of time... it really doesn't tell you much of anything. If you have oil temp, add pressure or vice versa if you ask me.
You would also probably need a bung welded onto your dp. But I believe its supposed to be done at least 12" away from the turbo. My guess is that if you didn't pay more than $200 for the a/f gauge than its one of the worthless gauges ("light show").
With something like an LC-1 wideband you can rescale one of the analog outputs to 0-1v range and use a narrowband gauge successfully and usefully.