not got a clue im afraid, never done a mk4 if you give me a while i could find out because someone i know has one, those points though, seriously if its a half decent sized amp as alpines normally are, in fact almost any amp will need a proper power cable of a given thickness. because of this
all the wire to the battery needs to be this thickness or you will effectivly get like a bottleneck effect, the standard wiring will not be thick enough i suspect. this is where i have gone in my mk3.


under the car may be an option if a grommet is really unavailable, ill look into it.