gotta watch that dim wire. even if you use a test light and connect test light clamp to dim wire to check earth the resistance in the park light circuit will give you a false earth. as test light only needs minimal amperage to illuminate it can do this without blowing the fuse, once you try to earth a 10amp head unit curcuit through this it's lights out, pardon the pun.
i've built some pretty intense car stereos over the years and still am, the best was my vs commodore weighing in at 128.3 dB, near blew my left eardrum (thought it was a speaker but later realised i could breate out thru my ear!!!!)
be careful with those blade terminals pushed into factory plug, no matter how much you secure them they will probably come loose and depending on plug terminal layout they may short out. my preference is aerpro adaptor looms, i know it's cheating but easy as!
d40 6 stacker is decent enough for now, would love to do something but money best utilised elsewhere for now. will be putting 7" dvd / gps screen with reverse camera (can't see real good past canopy). got a set of 3 way clarion comp splits and 2 10" clarion pro audio subs in the shed waiting for their call to duty but really, since the commodore the hearing isn't as good as it used to be sl they might be waiting a while.