I did mine last weekend...right if you look behing the battery theres a big rubber grommet with wires going through and theres 2 little rubber nipples coming off only about 5 mm long,pull one out with your fingers or long nose pliers,its quite awkward so be prepared for swearing..
Next thing is to get a welding rod,metal coathanger or someting like,i used a bit off an old wiper,you need something thin.get your vacuum pipe,i got a forge fitting kit so it came with the 5mm stuff and cut it to a point with scissors.you do this to make it easier to pass through the rubber nipple.
Next tape the vac pipe to the welding rod etc about halfway up,i used masking tape not elec tape it was loads better.
I also need to state....YOU DO NOT NEED TO REMOVE THE BATTERY TO DO THIS,like some said..i did mine on my own..
Right its time to get the rod into the car,go to the passenger side and remove to cover underneath the glovebox,2 thumbscrews.
Go to the engine bay.
Pass the rod into the nipple what you pulled off until it gets to the taped vac pipe bit then go to the passenger side,cabin to pull it through ,if you find the
tape comes off when you pull it try and be as neat and tight as you can with the tape.this WILL. pull through if you do it right.mine did 2nd go.
Once through you need to remove the passenger side cover on the feet area on the centre console,thinks a t25 ,then pass it through to the pedals,i find its easier to still leave it attached to the rod at this point.
I had a vent pod gauge so i needed to get it up there.so to remove the vent take to cover off the fuse box and just shove it out,theres nothing holding it in so just shove.
You will now be able to pass the vac pipe up there quite easily,be careful not to catch the pedals or steering rod etc..remove the welding rod now.
Next is the wiring,this is easy,all you need to do is earth it on the top screw on the fusebox,which is a nut i think,10 or 13mm,just remove a bit of the coating on the black wire,shove it behind then tighten the nut back up.
For the red wire i tapped into the light switch to get this powered up,to do this if you look at the fusebox area you can pull the light switch plug off the back without taking it out,you need to tap into WIRE 10,its grey,and theres numbers on the plug so you cant get it wrong.use a scotchlock to get your red wire to this safely and neatly.try the ignition to see if its working.this works on the switch so comes on whenever the lights come on not all the time.
Next is to get your vac pipe onto the back of the gauge, use a tiewrap to secure it on..
I would recommend the forge boost tap for under the bonnet for neatness and its fits lovely.
Build back up in reverse and jobs a good un`..
Hope this helps...
Andrew happy2