Alternator wiring

[347strokin]

I know I'm flooding this forum but all this little stuff has creeped up fast!

My PSI harness is wired to the LS3 alternator with an OEM connector.


But my factory truck harness has an alternator wire as well that used to bolt to the back of the alternator. It's also wired to an OEM connector. Please see pic.

My question is do I still need to connect the factory truck harness to the back of the alternator and should I just cut the existing OEM connector off of it?

Thanks and please let me know if this question makes sense.

I called PSI but unfortunately they won't have any customer phone support until July 10 and they aren't returning emails very quickly. Lol.

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[347strokin]

I guess it doesn't make sense to connect my factory truck harness to the rear terminal of the alternator. The rear terminal supplies power to the battery to charge it? Am I correct here?

 

[Honky Kong jr]

I guess it doesn't make sense to connect my factory truck harness to the rear terminal of the alternator. The rear terminal supplies power to the battery to charge it? Am I correct here?

Does your new harness have a light or gauge provisions? I'm not 100% on the newer charging systems but the older ones required a light or something to trigger the alternator to charge......or am I going way to far back?

 

[foamypirate]

No need to use the truck wiring EXCEPT that you need to trace the original alternator's output wire to see if it's providing power to the bulkhead (there are two power IN wires on TBI trucks). You need to make sure you tie it into a 12v power source with a fusible link, as close to the battery as possible. As far as the LS alternator goes, the harness connection and the battery output cable (directly to the battery or a distribution block as close to the battery as possible) are all you need.

 

[foamypirate]

Here is how I setup my wiring:

I have a heavy gauge wire straight from the battery, through a large fuse, then to a distribution block. From the distribution block, I power both power wires into the factory bulkhead, a wire to the junction block on the firewall for the HVAC, and a power wire to my LS swap harness.

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[Cuba]

In most alternators which include internal regulators, need to have some resistance to the field power wire. This is what turns on the alt. to charge after engine has started. 10ohms 6 watts resistor or just use an incandescent light bulb (which acts like a resistor) .... now if you have a cluster that already includes this, you don't need a 2nd resistor. ..

Does your harness already include? IDK. The main power on the stud of the alternator is different. That's the one that needs a fuse or fusible link close to the battery.

Maybe there's a way you can check the resistance from the 2 pin connector from alt. to cluster or battery gauge to verify some sort of resistor in that system. Maybe the gauge includes one? I don't know the rest of your set up to speculate.

 

[foamypirate]

In most alternators which include internal regulators, need to have some resistance to the field power wire. This is what turns on the alt. to charge after engine has started. 10ohms 6 watts resistor or just use an incandescent light bulb (which acts like a resistor) .... now if you have a cluster that already includes this, you don't need a 2nd resistor. ..

Does your harness already include? IDK. The main power on the stud of the alternator is different. That's the one that needs a fuse or fusible link close to the battery.

Maybe there's a way you can check the resistance from the 2 pin connector from alt. to cluster or battery gauge to verify some sort of resistor in that system. Maybe the gauge includes one? I don't know the rest of your set up to speculate.

The LS alternator is ECM controlled. As long as his harness has the pigtail for it, he's good.

 

[347strokin]

No need to use the truck wiring EXCEPT that you need to trace the original alternator's output wire to see if it's providing power to the bulkhead (there are two power IN wires on TBI trucks). You need to make sure you tie it into a 12v power source with a fusible link, as close to the battery as possible. As far as the LS alternator goes, the harness connection and the battery output cable (directly to the battery or a distribution block as close to the battery as possible) are all you need.

I'll trace the old alternator wire back and see where she goes. Hopefully that ties into the bulkhead to the "power in" wires.

 

[347strokin]

Here is how I setup my wiring:

I have a heavy gauge wire straight from the battery, through a large fuse, then to a distribution block. From the distribution block, I power both power wires into the factory bulkhead, a wire to the junction block on the firewall for the HVAC, and a power wire to my LS swap harness.

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I see what you did there. Makes perfect sense. I'm all over it! I just need to see a hats up with those "power in" wires on the bulkhead. Man, thanks again. This forum is the best. There's no way I could've down this swap without you guys.

 

[347strokin]

In most alternators which include internal regulators, need to have some resistance to the field power wire. This is what turns on the alt. to charge after engine has started. 10ohms 6 watts resistor or just use an incandescent light bulb (which acts like a resistor) .... now if you have a cluster that already includes this, you don't need a 2nd resistor. ..

Does your harness already include? IDK. The main power on the stud of the alternator is different. That's the one that needs a fuse or fusible link close to the battery.

Maybe there's a way you can check the resistance from the 2 pin connector from alt. to cluster or battery gauge to verify some sort of resistor in that system. Maybe the gauge includes one? I don't know the rest of your set up to speculate.

Thanks buddy! I think I'm good as all that is pre wired with the harness.

 

[347strokin]

The LS alternator is ECM controlled. As long as his harness has the pigtail for it, he's good.

Alright the old alternator wires lead back to one of the red wires and the brown one.

Then the other red one ran to a power distribution block on my firewall. I'm guessing these two thicker red wires are my "power ins". I'm just looking at schematics to try to figure out the brown wire.

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[347strokin]

The LS alternator is ECM controlled. As long as his harness has the pigtail for it, he's good.

Hey Foamy, when reading these electrical schematics, the equipment that have the dashed squares around them mean they're inside the cab of the truck?

Thanks again. Really appreciate this.

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[Cuba]

Ahh. Gotcha.

Hey Foamy, when reading these electrical schematics, the equipment that have the dashed squares around them mean they're inside the cab of the truck?

Thanks again. Really appreciate this.

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No the dotted lines mean they are part of another switch or assembly. They only show whats applicable for this circuit, but there are more connections to those dotted lined items. Not necessarily in the cab of the truck.

In this case, there's an ignition switch, a fuse block, & instrument cluster.

However all those "assemblies" are in the cab, I believe, including the fuse block which is below the column I think. In fact most automotive schematics don't specify underhood or cab. If you're lucky, they picture a grommet like those used for firewalls. Then you'd know.

 

[347strokin]

Ahh. Gotcha.


No the dotted lines mean they are part of another switch or assembly. They only show whats applicable for this circuit, but there are more connections to those dotted lined items. Not necessarily in the cab of the truck.

In this case, there's an ignition switch, a fuse block, & instrument cluster.

However all those "assemblies" are in the cab, I believe, including the fuse block which is below the column I think. In fact most automotive schematics don't specify underhood or cab. If you're lucky, they picture a grommet like those used for firewalls. Then you'd know.

Thanks Cuba. Slowly learning this stuff. The mechanical things are easy enough but electrical is a no go for me. Lol

 

[Cuba]

Hey, I learned a few things myself on this thread.

As for the electrical, practice makes perfect & with application it gets easier and more enlightening.