I'm looking for a place to buy an alternator around 140A. All the parts stores by me only have 105A. Also, i'm thinking on installing 2 batteries, and on my 90 firebird, on the passenger side in the engine bay, there's room. I removed all that emissions crap, and it looks like i can fit one there. I want that to power my 3 amps, but it'll be a **** load of cable from there to the hatch bay. Can i run it on the pass side? I've only seen it on the drivers side.

 

There's no reason you can't mount an extra batt.
Connecting it to the elec system can be a little tricky. If you simply connect it to the existing elec system, the alt will charge the batt that is in the best condition and the other batt won't get charged.

If you run 2 batts, you'll have to come up with a way to charge them independently. I've seen it done using heavy-duty relays and also with a marine type batt switcher.

 

here is a site that shows you how to hook up a Aux. Batt.

http://knightregistries.com/content/view/49/45/

 

Summit has some nice alternators for our cars I plan on getting one soon. From 105-200A there.

When adding an extra battery, be sure to fuse BOTH sides of the wire as close to the battery as possible. If (*** forbid) you get in a front end collision, the last thing you want is a battery blowing up under the hood. I have a battery on each side of my engine compartment, connected using 1/0 Power cable and 2 300A fuses.

 

Put your secod batt in the spare tire well. Then get a batt isolator rated for the size of your new alt run #4 awg batt cable to the isolator from their I would use #4 or 6 awg wire to the car batt and a #2 awg to the aux batt in the back of the car. This way will also help keep you from killing your car batt when you are just playing the radio and not runing the motor.

 

I like having a spare tire. I'm not too sure about mounting the battery back there. I got a spare battery, but it's a normal acid battery, and i heard those are bad to have inside.

 

I am putting the final touches on my dual battery setup. I put it in the rear set area. I used a 2001 Aurura set up with the battery so I do not have to spend 150 for a battery. Some GM cars came with the battery under the front set because there was no room in the engine campartment.

I recommend going to a battery store and having all your cables custom make. this will ensure the type of set-up that you want will work.