Wiring up an Amplifier

I haven't been the type to go crazy with my stereo setup but I saved the speakers, head unit, and amps from my last car whose previous owner had a need for more sound. I have the speakers mounted and audio cables run to the trunk and I will be using two small amplifiers, one to run the front and one to run the back speakers in the car. I ran all of those cables down the passenger side of the car, which so happens to be on the same side as the battery. I want to run my power cable to the trunk now and I hear it is a bad idea to pass the power cable near the signal wires. So, since my alternator is on the drivers side, and has a conveniently located fuse for adding a cable, can I run my power wire for the amps from there? Or will that cause even more interference that running past the signal wires? (I have an additional fuse to run just for the audio equipment)

Power from Solenoid (pass) or Fused Alternator (driver)

You could run it there. You might need to run a Cleansweep to clear out the interference, but if you use heavy enough cable (0 gauge welding cable is good fun) with good enough sheilding, it shouldn't pose much of an issue.

You can't get the signal wires that far from the chassis which is really one big negative power cable so it's somewhat academic trying to get the signal wires "away from power".

Unless welding cable is cheap that seems like massive overkill and it's harder to route and pass through bulkheads / floors / etc. What's the fuse on the amplifier, 30A? 40A? Use that as a guide for your cable selection then go for whatever solution is cheapest.

The real issue is having good connections made with proper termination hardware and then having good grounds, I think, but I've not fought with audio installations enough to stop noise.

I agree that this is effectively being 'overthought'.

I would not worry about running the power and signal wires near each other. I almost always do that and ive never had noise from that.

Isolate the signal wires from the power wires in their own corrugated tubing and tie them together. I have utilized this method hundreds of times with no issues. People make the mistake of zip tying the B+, NEG, Switched and signal wires together without any protection. Make sure you run similar sized ground wire as your Battery Positive and make sure to run a common ground from your head unit to the amplifiers ground as well as to the dash ground. Ground loops are funny animals, they tend to live in the distance between the head unit and amplifiers.

I concur noise from the power wires is a non issue unless there is something wrong with the system to begin with. You are much more likely to get noise from the ignition system, but most likely you will just get the noise you want to hear.

Cars are a noisy place anyway, I always am amused by how much trouble people go through for quality, as long as you have enough power and no distortion then things will be fine, damn the noise, its a car, its gonna be noisy.

I've not heard of a plastic corrugated tubing being effective at harnessing and carrying EMI away from internal wiring. If you want to try going this route, a metallic cable overbraid with termination to a good ground on the head unit side of the signaling cable run could be used in an automotive environment.

Which is a solution used in aircraft for protecting signal wires from EMI but I've not seen it done in a car. There should be other ways to do this but everything I can think of involves terminating cable ends by hand and I'm really not hot on doing that myself. And the thing about battery + or the turn on wire for the amp, et cetera, those are all DC power so they shouldn't induce hum.