So, decided to fit my boost gauge to the car today and thought i take a few photos along the way, not all are very clear, but hopefully the idea will get across. First I had to locate a place to put my pvc tubing through the firewall, luckily i found a hole hat was in the firewall, it was meant to have a gromit round it (it is the bonnet release cable) so just pushed the tube through and sealed it with silicone sealant. Where the wiring goes through the big grommet there are two smaller holes,