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I am upgrading my 70 chevelle from a 12si 94 amp alt. to a cs130 alt. If I choose to use a 140 amp alt. vs. a 105 amp will I have to do any different wiring mods to the car that I wouldn't have to do if I used the 105 amp cs130?

I am running 8 gauge wiring from the alt. to the horn relay and back to the junction stud next to the battery and I’m upgrading the fusible link and wire size from the junction stud to the battery.

I already have the electric fans wired up using the appropriate circuit breaker/relays but I need more juice at idle and the 12si just isn't cutting it. I figured I might as well use a 140 amp alt since the difference in cost over a 105 amp isn’t substantial as long as I don’t need to worry about any addt’l wiring.

One last question: Can I run the 8 gauge wire from the alt. to the junction stud next to the battery and then run an addt’l 8 gauge wire to the horn relay from the junction stud? I was hoping to do this instead of going from alt. to horn relay and then from horn relay to stud.

Thanks,
Jason
 

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Well... are you a gambling man Jason? Do you feel lucky?

For starters the electrical system is fed from the alternator and not the battery. A very common misconception that you have to rework all of the battery wiring when you upgrade the alternator. In fact there are reasons to leave the factory wiring from the battery to the horn relay bus bar alone. These particular wires do provide power from the battery to the electrical system but only when the engine is not running. Thus the load is substantially reduced. Further when the engine IS running these wires do nothing more than carry battery charge current. Not much is required here and too much can be a BAD thing. So using the factory wiring will provide a current limit.

Now for the alternator power feed wire where things get much more interesting... on one hand this wire will only carry as much current as your electrical devices demand. So if you have 70A of load you will only see 70A of current no matter how much your monster alternator can put out. This suggests you need not increase the size of this wire. Then again should your electrical device demand exceed the capability of the wire, and you have not upgraded the wire, then the alternator will gladly provide enough current to let the smoke out of the wire. This would be a BAD thing ;)

So I recommend upgrading the power wire from the alternator to the horn bus bar only. Leave the other battery to bus bar wiring alone. And when you choose the wire shoot for around 4g wire. You may find this URL pertinent and interesting:

http://www.powermastermotorsports.com/charge_wires.html

A good idea would be to add a 175A mega-fuse assembly inline with this wire to the horn bus bar. This will provide protection against a battery-powered short on this very high power wire. American Autowire is one of the few suppliers that I have seen that has suitable fuse products for this application.
 
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