I'm going 4-way active

And to do that I need to run separate leads to the tweeter and the midrange on the premium system, as they by default are connected in parallel like so:



The easiest way to do this seems to be finding the splice between them, and then cut the wires going to the dash and hook them up to a new set of wires going to the trunk.

Does anyone know where to look?

 

Wow, active means separate amps for tweeters, mids, and lows as the signals are filtered before it enters the amplifiers? so one amp per speaker. In an active scennario there is no way you can use the existing wiring as all the wires have to come straight from the amplifiers to the speakers.
or do you mean one amp ->frequency filter -> on a 4 way component speaker set?

In my case I disassembled the frequence filter, and put the components directly on the respective speakers as I didn't have space to accommodate the filters either in the doors or in the central armrest and I didn't fancy running new cables.

 

Yes, one amp channel and a digital crossover for each speaker.

To do this I have a JL HD900/5, a digital T-amp (to drive the tweeters) and a JBL MS-8

 

4 way active means that you need 4 ampls per channel, not 1. In that case you shouldn't be bothered about the existing wiring and run complete new cables from each amplifier to each speaker unit.

Anyway, from the central arm rest the split is done to each speaker and depending on the year of your car and standard or premium sound system the pre laid cables might be change.

 

Depends how you define channel I guess, it means that you use 4 speakers to cover the freq range of interest, all digitally equalized.

I'll dig around under the armrest e

 

Ok, the splice is hidden well behind the front panel, so the easy solution is to run a new cable from the dash, removing the part underneath the steering wheel on the left and removing the screws holding the glove box in place on the right. Easy