connect multiple items at +12v in fusebox

If you have any kind of stereo system with an amp you should have already have some 8 gauge or bigger going thru thru firewall, just go thru there,,,,if not, then there is no better time than the present to get that right angle drill out and put a nice 1/2"-3/4" hole in there, for this wire and any future wire you may need.................drill it, drill it, drill it, be sure to use some loom over the wire in the engine compartment

OK It's either a  a Golf or A3 basically or a Polo, if you can't see any grometts, 1) Look at firewall behind engine block, 1) If it's an auto there might be a gromett where the clutch cable would have gone through or behind the ABS box, as a last resort look up where the wiper gear is located, there might be a way in through the to the internal fusebox. The gGolf has a big nasty to get at gromett where main loom goes through but it hass niples you can cut off and get through. This is assuming it's a current shape

Thanks for the pointers so far guys. I have had a good look at how I might get a wire through the firewall, including underneath and this is what I have come up with... I think I have three options. Try force the wire through the big hole in the existing rubber grommet. Make an additional hole in the big rubber grommet. Or drill a new hole via the hole on the left. I believe there is enough clearance behind there, the only thing is there is sound proofing material behind it. Would be much easier on the driver's side though :)

Bottom picture left hand grommet.  See the nipple on the right side of said grommet?    Cut it off and run wire through hole.  That is why they are there.