3 Wire Alternator Help

I know this has been discussed before but for whatever reason I'm still having trouble with my Delco 3 wire Alternator swap. From my research it sounded like I needed a fat wire going from the positive terminal of the battery to the positive post of the Alternator, with a jumper wire going to pin 2. Then an ignition wire going to pin 1. Then a small wire grounding the Alternator. I guess I'd need to add some sort of fuse in line with the positive wire to the battery unless that is internal. But that layout doesnt seem to make sense with the posts on this alternator, the positive post is pretty small, and theres another fat post on the other side that is unmarked. Does anyone have some photos or diagrams of how to hook these alternators up?

 

Would this be correct?

 

Yes.

 

The BAT terminal on the rear of the alt usually has a red insulator under the nut.

 

Yeah I guess I just expected the positive wire to need to be bigger since it's a 90-something amp Alternator. Looks like it's only needing about a 10ga wire for that little positive post.

What about an in line fuse? Is that internal to the Alternator or should I add one external?

 

Bigger wire gauge isn't ever going to hurt on that cable. I personally think 10 GA is a bit too small, but lots of folks do it, and don't seem to suffer any ill effects.

 

Not recommended. Just another trouble spot to contend with as in corrosion getter.

 

There should be a diode in that charge light wire.

LOTS of good info here:
Catalog (madelectrical.com)

 

That extra bolt on the backside of the alternator is what was throwing me after all. It turns out it is for mounting to GM style brackets that we don't use in jeeps. It looked to me like a wire terminal of some sort and I couldn't get my head around what was supposed to go there.

A question about the ground for this alternator - is it enough that the alternator is bolted to the motor and positioning bracket? Or do you like to run a ground wire to one of the body bolts of the alternator as well?

 

Mine has been running grounded through the mounting bracket for well over a decade at this point.

 

If you have a good ground strap between engine and frame, that should be fine.
Otherwise, run a ground wire from alternator to battery. That's what I do with the 12SI.

 

That's how mine is but I have a set of cheap old jumper cables (positive and negative) running from alternator to battery with terminals onr the ends . Good positive cable to starter and ground straps from frame to motor and body tub to battery. That metric hole on the back is what I used for the ground cable.

 

I have a 110 amp off shore alternator on one of my motors, I ran 8 gage wire to the amp meter and the battery and 8 gage ground to the battery just to be sure all is good. No problems yet. I use Marine wire as it is more weather resistant.

 

Not needed with the Ign light.

 

Appreciate the info. This is one of those things that evolves from replacing a component to re-working your whole electrical system. My ammeter has been out for some time now, and I don't have an indicator light. It also appears my battery is grounded through the winch, which isn't ideal! I'm going to check my engine ground strap and replace if needed, then direct ground my battery to the frame, then run some nice fat positive/negative wires from battery to alternator, and add a circuit for the ammeter and indicator light.

 

Is that because the light acts as a diode or has an internal diode?

 

It is because the bulb resistance drops the voltage going to terminal #1 of the internal regulator.

 

If you follow Mark's instruction for wiring in a 3 wire 12si alt you will be very happy. The whole Idea of wiring in the correct way reduces voltage drop. Makes everything work to peak performance. I put a junction block on the firewall where the heater was. Ran an 8 ga red wire with a fusable link to the hot side of the starter. Positive cable from battery to starter. Battery ground to alt.
The alt has a plug with a red and black wire. The red wire is the voltage sensing wire and should go to the junction block.
The red wire on the post alt post goes to the ignition. I can't remember where the blue wire went but I can find out. If you talk with Mark at M.A.D Electric he can answer your questions.

PS mine is a little different than some but works well.

 

This site has a bunch of great articles about electrical stuff.
http://www.madelectrical.com/