Could someone please post a diagram or explain the correct way it should be plumbed in on a external wastegate please

 

You can run it just like internal or run it like they describe the external setup for the Profec B Spec II. I believe it is pressure source to lower (separate from the source that goes as input to the 3-port) and com port from the 3-port to the upper nipple (on top of the WG).

You can see the manual here http://www.alamomotorsports.com/gred...EC_B_SPEC2.pdf

 

the side of the gm with one port is your boost source, then the other nipple on the gm without the foam filter goes to the BOTTOM of the wastegate (tial), the top is left open to the atmosphere

 

It seems like they are 2 ways of which you can plumb the external wastegate. Which way gives the better boost response.