I found a fitting on the bottom side of my turbonetics turbo that was not capped and had no line hooked up. Can someone tell me what this fitting is usually hooked up to and should I cap it off? Thanks

 

Its mainly used as a boost reference source for a boost controller (be it manual or electronic). Its something that is optional to use, because sometimes that nipple is too strong a source.

If you don't plan to use a boost controller now, just cap it off with a closed end of vacuum hose. You'll be just fine.

 

Thanks for the help