Amp Power cable size.
 

Hey RS;

I'm going to be helping a friend do a sub install soon, he has a used Kicker BassStation either 10 or 12.

The proprietary harness from the built-in amplifier has been cut short, so new wire will have to be soldered extend the stock harness.

The amp and sub setup is only 90w rms, as stated in this document here:
BassStation Instruction Manual (PDF)
This suggests that I'm not gonna be able to use a standard amplifier installation kit, as they're rated for 500w+.

The photograph here suggests that the stock harness uses a much thinner gauge than even 8AWG, all the way to the battery, and a 15a (according to the manual) ATO fuse in an in-line fuse holder.

My question is, what kind of wire is best suited for this application?

Another question, for tapping into the rear speakers of his '13 Kia Forte Koup, do I tap at the wire or at the speaker leads? What's the best kind of way to do that tap?

Thanks guys.

Odds are it uses 12 AWG or 14 AWG for a 90 Wrms amplifier.

Stick with the similar gauge wiring it came with. Going to a thicker gauge won't really benefit you anyways. Make sure it's copper wire and not the cheap stuff.

As for tapping into the rear speakers, taking signal from the wire is usually easiest. Best way is to solder to the wire to ensure things don't come loose. T-taps tend to suck and wiggle loose over time.

I don't want to sound like a dick, but...
Your friend with a new car wants you to modify his (with warranty) car and these are your questions? How hard could it be right? I gotta wonder what will happen if there is a problem.
Car stereo shops exist for a reason. We have insurance. We have the expertise to tackle these jobs (which may seem simple) in a timely, professional fashion. We look at how your mechanic will need access to places that you may or may not install something. We have experience in how to mount things so that you can use your car as normal.
I'm not saying that you won't do a fantastic job, I'm suggesting that you might want to practice on an older car first. When we are training new installers, we won't let them touch a new car without lots of practice first.
This forum is full of information and I'm not saying that you HAVE to come to SoundsGood. I'm suggesting another look at consequences prior to possibly voiding this friends warranty.