Pick a vacuum port on the throttle body or intake. You can hook it up on any vacuum port on the car, which is not blocked off.

If you hook it up on the manifold, you'll get actual boost pressure past the intercooler. On a small turbo/larger motor combination, such as mine, which is tapped in that way, you'll actually see the boost fall off at higher RPM's, where the turbo isn't pushing enough additional air to keep up the 18 lbs it spikes at, when the motor is using a large quantity of air itself. It will actually fall to around 13 psi on my car.

You generally won't see that problem with a big turbo/small engine.

Ideally, you'd monitor it in two places. You should monitor the boost, technically, at the turbo. There are usually boost reference ports on the turbo, including, but not limited to, the wastegate reference port on an internally wastegated turbo. This number is likely to be higher than the MAP boost, and will give you an indication as to the backpressure, and the efficiency at which the turbo is operating. In my case, the backpressure is quite high, and the air is quite hot coming out of the turbo, as the motor is big, the turbo is small, and it's choked pretty badly. This is why it quits supplying air, and falls off at higher RPM's.

But, for those not so technically inclined as to want to know that:

Just tap it in to a vacuum port on the throttle body, or on the intake manifold. There should be plenty of emissions lines there you can choose from.

 

go to any of the manufactures website