When I did mine. My goal was to make the system capable of safely and easily running a significantly higher accessory load without permanently altering the factory layout. I essencially added a high amp circuit to feed everything and mounted it under the hood. As you know, the battery only starts the car, the alternator feeds your electrical system when the car is running.

In a nut shell, I created a new high amp circuit that starts from a modified AC Delco CS 144 with remote voltage sensing, and is fed to a main distribution panel that feeds all the high-amp draw circuits I added under the hood.

The car's original main electrical circuits are fed from the main distribution point just like another circuit. I have no high amp draw inside the cockpit or the rest of the car.

Everything is fused, all the sub-circuits, all the main power cables everything! I use relays on all high amp draw items including the headlights, fans, fuel pump, a/c, etc.

The rest of the car's original wiring is fed my high-amp underhood main circuit, but since the headlights and a/c blower are fed under the hood, only low amp circuits remain inside the cockpit. These are fed via the original amp guage circuit, or main power fed through the factory bulkhead. I bypassed the amp gauge and had my amp gauge converted to a volt gauge. Aside from the healight and a/c relay circuits, the amp guage bypass is the only alteration to the factory wiring inside the car.

My battery is in the trunk. I have a high amp fuse protecting the main power cable, full time. My fuel pump is fed via a fused, key-switched, oil-pressure cut-off switch protected dual 40 amp relay from the battery.

The entire "added on" electrical system can be easily removed and returned to stock configuration in a short time by taking out all my add-on stuff, mounting the battery and cables back in the stock location and simply replacing and plugging in the factory underhood wiring harnesses. I'd also have to replace the factory amp gauge and remove the headlight and blower motor relay wiring etc.