Alternator Wiring

[Dwall174]

I have a 1977 Chevy pick-up 4X4 and I want to upgrade my stock 65-watt alternator to a 200-watt unit, I’m also going to add a additional battery & isolator to the system. I’ve read that with the high-out put alternators you should also change the wire from the alt. to the battery.

My only positive battery cable goes straight to the starter which has the starter solenoid mounted to it. A smaller wire maybe “10- AWG” runs from there into a wire harness then I believe into the main fuse block. It looks like the same size red wire then comes out and goes to the alternator.

Being that I’m going to be adding a second battery & the dual battery isolator, Can I just run a 4-AWG wire from the back of the alternator to the isolator? If so do I connect the original wire to the alternator stud or to the isolator?

[TwentyTwo-Zero]

I think that the wire you are looking at is the one that goes to the dash for your amp meter/idiot light. If it plugs into the alternator (actually "plugs" in with another wire in the plug beside it) that is not the wire you want to replace. If you look at the back of the alternator there should be an (isolated) threaded stud that has a thick wire retained by a nut. It should run from there to the positive cable at the battery. This is the wire that you want to replace with a larger gauge so that it doesn't restrict the output of the alternator to the battery. You can make one yourself, or check out a stereo installation/high performance/electrical shop - they might have a ready made one that is a direct replacement.

[Mad Bomber]

OK, If you look at the back of the alternator, there should be a 1/4" or 5/16" stud sticking out of the back of it (see picture). This is the alternator output. If it is an internally regulated alternator, this will be the only wire coming out of it. If it is externally regulated, there will be two more wires coming out, usually smaller wires like 14ga. The stud is where you want to attach your cable, and run it to the battery. You can leave the stock 10ga wire, as it probable feeds truck accessories, and just add your larger cable on top of it.

Alternator Stud:
[ external image ]

[Dwall174]

OK, If you look at the back of the alternator, there should be a 1/4" or 5/16" stud sticking out of the back of it (see picture). The stud is where you want to attach your cable, and run it to the battery. You can leave the stock 10ga wire, as it probable feeds truck accessories, and just add your larger cable on top of it.

Alternator Stud:
[ external image ]

Yea that's the wire I was talking about! It's probably only 10-AWG & is the only wire coming off that stud. The alt. does also have that small two wire plug that 22-0 was talking about.

[Dwall174]

Check out [Please login or register to view this link] My truck's wiring is like the second schematic just above the "Ignition Switch Wiring for 1977"

[Mad Bomber]

Yeah, if I am reading the schematic correctly, the wires numbered 1 and 2 are the voltage regulator wires. Leave these alone, because if you hook them straight to the battery, you could fry the regulator. The wire labeled "Bat." goes to a distribution block on the firewall which also feeds the ignition switch, as well as something else off the screen. (see Diagram 1) What you need to do, is add your 4ga wire from the Bat side of the alternator to the + side of the battery. Leave all the stock wiring there, just add a "Jumper" as it were to aid in battery charging. (see Diagram 2). I would run all high amperage accessories directly to the battery, and this way you won't fry any of the stock wiring in your truck. It could be a nightmare to track down a short or burnt wire in there, and once your car has electrical gremlins, it will always have electrical gremlins.

Diagram 1
[ external image ]

Diagram 2
[ external image ]

[Dwall174]

Ok I guess it would be the third diagram that is like mine! The way I read it the first two were the same schematic just different views?
Anyway I will try to post a pic of how my system is running. It's hard to be 100 % sure because of it going through the wire harness! But this is what I believe I have. [ external image ]

[Mad Bomber]

Ok, then yeah, it would still be the same to hook it up, just run a wire directly from the alternator post, to the isolator, or to the battery. Either way you look at it, its the same basic idea.

[Dwall174]

Thanks that’s what I was thinking also!
I’m going to add a in-line fuse to that stock 10-AWG line just to be on the safe side. :D

The way I see it if the new 4-AWG should happen to come loose then the 200 amp alt. would try to charge the battery through the 10-AWG wire.

200 amps going through a 10-AWG wire into a 30 year old fuse-box would sure let those gremlins out!

[jessejamesdallas]

The set-up you have, is basically the same one I had on my 2004 Ford van...When I up-graded to a 250amp alternator, all I had to do, was disconnect the wire from the alternator that ran to the starter, and install the larger gage wire straight from the alternator to the battery...Leaving the original wire still connected to the starter, but the end that originally was connected to the alternator, I just taped-up the end, and used plastic tie straps to stick it out of the way of anything...

This way, the alternator first feeds the battery via the new larger cable, and then feeds the starter threw it's original wiring...

One thing to remember, is your not changing the volts by going to a larger alternator, just the amount of amps it produces. So to carry the extra amps, it's necessary to go with larger wire, or the wire will burn up from over heating...And anything that's regulated for 12 volts (starters, radios, lights, regulators) should be OK with the increased amount of amp's.

Your just wanting more amp's to go to the battery itself, for the extra load of your box.

So in short, all you need to do, is not use the wire that go's to your alternator now. Disconnect it from the alternator, and tape-up the end. (don't remove)

Then get your 4 ga. wire, and run it from the alternator, straight to the Pos. on the battery...That's it...