I am wondering where the front door speakers wire splits into 2 seperate wire sets to power the tweeter and woofer...
Is it inside the care or inside the door? to save me taking both apart.
as above, the wiring is inside the door.
*1 set of wires (+ and -) pass through the multipin connector into the door
*wiring goes to door woofer; tweeter wired in parallel off the woofer
*xover for OEM speakers: no lowpass filter for woofer so this essentially receives a 'fullrange' signal, but relies on its natural 'rolloff' (ie: inability to play treble); tweeter has a simple inline capacitor for its highpass filter to remove the midrange/bass
fitting aftermarket speakers can indeed be a pain. IF you want to fit an aftermarket tweeter into the factory position, it is easiest to mount the new xovers in the doors as mentioned. keep them between the doorcards/trims and the thin white splashguard foam (to avoid exposure to moisture).
however, also consider mounting the tweeters in the cabin, say at the base of the A-pillars or down in the kickpanel areas and angled upwards-inwards. the factory positions don't provide the best imaging/soundstage, so if you're keen, experiment with tweeter-position/angle. of course, there are cosmetics to consider, which may be a priority to you.
My amp wires go down the centre of car to head unit and was hoping to use a male iso connector and use standard oem wiring where possible as from what i read rewiring is a bit of a nightmare!
"amp wires"? can you explain this further? are they the powerwires for your amp or the RCA cables or what?
in general, keep any RCA audio cables distanced from wiring looms and amp powerwires, to avoid EMI (electromagnetic interference)/'noise' entering the audio signal, which can manifest as annoying 'engine whine' (highpitched whine that alters in pitch with engine revs). in my old 156, i ran the powerwires down the left-side under the doorsills. audio cables when down the centre. speakerwires are not susceptible to EMI like RCA cables, so can be run under the doorsills too.