PLEASE HELP
 
I T-intersectioned the piping going from the turbo. This means both the stock gauge and my aftermarket one should work right?
Now both of them are only just hitting 1PSI at full revs! How can I fix this?

personally I wouldnt tee it off there..
 
Maybe try and connect the new boost gauge to one of the blocked vacuum ports at the back of the intake manifold, that way you are getting the amount of boost in the actual manifold.

Oh really? Where exactly are these ports? I cant seem to find them?

believe they are behind and under the manifold near the boot/firewall. I think both are blocked off with banking caps.

http://i.ebayimg.com/t/JDM-Toyota-MR2-Turbo-3SGTE-Intake-Manifold-SW20-MK2-/00/s/NjgzWDEwMjQ=/$(KGrHqV,!h0E8KMe(SSSBPD4SwV6D!~~60_35.JPG

Thanks heaps! I'll try them!
 

Check for cracked hoses etc?
 
I T'd mine at the map sensor IRRC. Like beagle said, the turbo is probably not the best place for it.

It shouldn't really matter where you tee it off from as long as its close to the plenum, but you might as well use one of the spare ports.  To try an easy location quickly tee off the tube to the MAP sensor.  
 
If you are only seeing 1psi on the guage under load/revs then I would say either your gauge is faulty or you have a leak somewhere in the feed to the gauge and/or fitting.  This of course is assuming your motor/turbo is sound.
 
When I hooked my gauge up I used thin plastic high pressure tubing (around 3mm), being thin its easy to route through things and theoretically the gauge remains very responsive even with a very long hose due to the small volume of air present in the feed line.
 
Cheers