Reegster

Big custom builds are EXACTLY what I love most about car audio. This makes me smile.

Run a battery isolator if you plan to add extra batteries in your vehicle. I would think that you amp cutting out is a capacitance problem not a grounding problem. Running cable from the front of your vehicle to the back is fine for the 12v+ but the entire body and chassis is a ground. A long ground wire directly to the battery might get you slightly better power (SLIGHTLY) but it will very likely cause inducted noise. 95% of inducted noise is usually from improper/poor grounding in a DC electrical system. Burp trucks and SPL guys don't give a rats ass about engine whine, alternator hum, or ground loop noise. They are not listening to the system for audio quality, they are looking for max output. They can run multiple long run ground cables if they want (again only a minor improvement electrically) because they don't care if it creates a small amount of whine or hum. As previously prescribed: definitely do a big 3 upgrade and also consider adding a capacitor.

Realize this is a reply to an old post, but for the sake of those reading this after the fact who may have the same question, if you supply 9v (little square battery) to the speaker leads (disconnected from amp) both subs should push out and stay out or pull in and stay in while the battery is connected to the leads. This way you can visually confirm their polarity is the same or out of phase with each other. Hope that helps!

Put a Mechman HO alternator on there with a battery isolator and add one or two gel-cells or lithium power cells. Run your audio gear and 12v-16v accessories off of that, you'll have zero problems. Big 3 goes without saying.

Honestly, you don't need a mechanic, any reputable audio shop or aftermarket parts dealer can do this upgrade for you no problem. I doubt they'll let you hang out and watch. I'd be very cautious about letting some guy off the web come by and do wiring on my car. If you look on youtube there are dozens of big 3 upgrade videos. You can easily do the job yourself with some very basic tools. I'm in Canada so I can't talk to prices where ever you live, but if you take it to a shop it should be $400 or less for a professionally done big 3 upgrade. Good luck!

The high current battery in your truck should have plenty of output for your 12v-16v audio equipment etc. You might just want to add a gel-cell or lithium power cell for your aftermarket stereo and accessories. Don't add mechanical devices like alternators or stators to electric vehicles, you'll have inducted noise and ground loop problems just to get started, other more serious complications are possible/likely.