10si Alt Wiring ?'s on 1960 Burb

[MASTERBrian]

I'll start with this truck was DOA when I got it, so I've never been able to test much of the electrical but I did have working lights and horn. The truck was converted to a 10si Alt when I bought it, BUT I'm not certain it was wired correctly. I've got the new motor in, converted from points to HEI and I've re-wired almost everything in the engine compartment. I do still need to do the horn and headlights AND this Alternator. I've also asked some other wiring questions in other threads that hit on this a bit, but still curious, and I want this to be Alt only.

So, there is a 10 gauge, non-fusible link wire coming directly off the + terminal of the battery to the Alt BAT terminal. Then the 2 plug harness has the red wire going to the BAT terminal and the other wire is cut. From what I've read this is wrong in several ways.

First, I read that instead of going to the Battery, the wire going to the BAT terminal on Alt should go to the terminal block, typically at the starter, so that the Alt isn't just charging the battery, but supplying the entire electrical system with power. Other thing is I realize it needs a fusible link.

Second, I get mixed things on the Red wire, from 2 wire plug, I thought I read somewhere it should go somewhere under the dash, but can't recall where!! ...maybe the accessory power terminal? But I also see a lot of posts/diagrams that show it just jumping to the BAT terminal on the Alt. Which is correct?

Third, the brown wire, which was cut should be wired to the idiot light in the dash....where do I pick up that wire? Is that a wire that used to go to horn relay? I've seen illustrations where they cut a blue and brown wire on that harness and wire them together and hook this wire to it. No clue what year as the parts look different. I also see people installing resistors, etc....I'm thinking that's only if there isn't an idiot light.

With all of that can anyone clarify a little?

-Is 10 gauge wire with 12 gauge fusible link large enough to come off Alt to the starter junction? Should it be larger? I have some 8 gauge wire I believe.
-Does the red wire in harness just wrap back to the BAT Terminal, if not what size wire does this need? 10 gauge?
-For the brown wire, if I tie it into the idiot light, is 18 gauge the correct size for this?
-I also have a Battery Level Gauge, how does this fit into this mix or does it not? I'll try to post a pic of it later.

On a bit of a side note, where the harness leaves the firewall and enters the engine bay, they spliced a 10 gauge w/ fusible link wire onto the Red wire going down to the horn relay, this was hooked to starter BAT terminal, not sure if they changed much else down there. Do I leave that alone or would this be part of the mix?

[Dead Parrot]

What the PO did was make a homemade 1 wire alternator. The red wire from the 2 wire plug goes to the junction block as does the Bat wire from the alternator. The red one from the 2 wire plug is a voltage sense wire and lets the alternator allow for voltage drop in the main wire. The other brown wire is an excite wire. Some alternators have an internal resistor that accomplishes the same thing.

Normal difference between fusible link and protected wire is 4 gauge sizes. So your 10 gauge wire should have a 14ga fusible link.

You should be able to purchase a premade main alt wire with proper fusible link or recover one from a newer vehicle at a salvage yard.

If the alternator is a 10SI, might as well swap for the 12SI now. Same size but better output at idle.

[MASTERBrian]

Originally Posted by Dead Parrot

What the PO did was make a homemade 1 wire alternator. The red wire from the 2 wire plug goes to the junction block as does the Bat wire from the alternator. The red one from the 2 wire plug is a voltage sense wire and lets the alternator allow for voltage drop in the main wire.

So, off the alt BATT terminal run to the distribution block at starter, unless I add a remote one. I'll also run the Red Wire to the same location. Both wires will be 10 gauge with 14 gauge fusible link(s).

You mention voltage sensing.....I also read somewhere about a sensing wire....is that a special wire? Or is any 10 gauge wire going to work?

The other brown wire is an excite wire. Some alternators have an internal resistor that accomplishes the same thing.

The brown wire (actually white on my pigtail) it'll run to the idiot light.
I thought that all I, as in 10si or 12si, alternators where internally regulated...is this something different that what you are mentioning?

Normal difference between fusible link and protected wire is 4 gauge sizes. So your 10 gauge wire should have a 14ga fusible link.

You should be able to purchase a premade main alt wire with proper fusible link or recover one from a newer vehicle at a salvage yard.

If the alternator is a 10SI, might as well swap for the 12SI now. Same size but better output at idle.

Got it on the fusible link, some things say 2 sizes smaller, but I'll go 4.

I'll look for premade, but doubt I'll find. I could run by salvage yards, but that's an hour+ commitment....any reason not to just make these with the 10 gauge wire and fusible link? Is there something special about premade?

I plan on updating to the 12SI at some point, but for now, I'm just trying to keep costs down and get her on the road. Since I already have 2) 10SI's figured I'll run them until they break or I start adding accessories, which will probably start as soon as she's back on the road.

[MASTERBrian]

Just read something else that mentions running a 6 gauge wire from the alt to handle more current. I might look into that, even though I realize my 10si won't put out that much current. I have a length of nice 6 gauge write left over from amp install on another car from years ago. I'm assuming I'll still run the red wire from harness as 10 gauge.

I'm sure at some point, I'll add a stereo (no sure how crazy) and other things that might be juice happy.

[MASTERBrian]

Here is a pic of my ammeter.

If I'm not mistaken this is wired on a separate circuit from the idiot light, is that correct?

From the diagrams I am finding the idiot light is off the brown/white wire talked about above, whereas the ammeter is wired into the battery side of things.

[VetteVet]

Sure looks like a voltmeter to me.
They are also wired on a separate circuit than the ammeter. The hot side goes to a key on, voltage source, and the negative goes to any good ground.

[MASTERBrian]

Originally Posted by VetteVet

Sure looks like a voltmeter to me.
They are also wired on a separate circuit than the ammeter. The hot side goes to a key on, voltage source, and the negative goes to any good ground.

I knew that was wrong when I typed it but was in hurry to get out the door. It is voltmeter.

The other strange past is the switch next to it. Kind of cool switch, but all it seems to do is turn on the lights of the gauge. Why they didn't hook out to the other lights is being me, but maybe someone can fill me in. Sure has a lot of wires for simple switch...

[Dead Parrot]

Yes, both the main Bat wire and the red sense wire go the the same junction block. I recommend you use a 8ga Bat wire with 12ga fusible link. The sense wire doesn't carry much current. 12-14ga should be enough for that. The brown wire is used for idiot light signaling but the bulb also provides a path for 12v battery to flow back to the alt to excite the alternator. If the alt isn't generating, the brown wire has 0 volts and current flows from the battery, through the bulb, lighting it, and into the alt. Once the alt is generating, the brown wire has 12V on it that balances the 12V from the battery and the bulb goes out. In a gauge vehicle, the bulb is replaced with a resistor.

A junction block from 90s truck should make a nice upgrade. If getting one at a salvage yard, be sure to get all the wires with it since they come with the proper sized terminals and factory fusible links.