I covered this a while ago. I drilled a 5/8" dia port through behind the battery and fitted a grommet. You could go up to 7/8 with care. Start small. There is a lot of insulation to drill through too. The internal fibreglass insulation will wind up around your drill bit. Do it a bit at a time. Be patient.
The position has to be quite precise. There are two air-con pipes passing through the firewall. You have to drill at a point ~25mm (+/- 5mm) right of a centre line drawn between the centres of these two pipes (as seen when facing the firewall when standing in front of the car with the bonnet open) and at the same level as the midpoint between the two pipes.
Remove your battery so you can manoeuvre the drill and keep it straight, perpendicular to the firewall, and remove the glove-box so you can see the inside where the drill comes through, and drill a small pilot hole first. There is also a small bit of external soundproofing to push to one side at this point inside the engine bay.
I have run my boost guage lines and my other leads through this one port. Don't forget the grommet or cable ducting or the cables etc will chafe. You can access the hole from inside the glove-box aperture when the box is removed so you can feed wires both ways easily.
No responsibility taken if you mess it up or drill through something critical. It works fine for me.
Last edited by Doug_MPS6; 17-10-2010 at 10:49 AM.
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