Alternator wiring help

[broflow]

So I'm admittedly not fond of wiring issues so here goes. This is on my 78 K5. As far as I know the truck wiring is original. I went to a serpentine setup off of a 4.3 out of a newer style mini blazer. I currently have the alternator that came on it. This alternator has 1 post and 1 plug that only has 1 small wire coming out of it. I guess I'm wondering where I need to go with my existing wires? Would the 2 wire from the trucks flat plug and the single wire with the rubber boot all go onto the post connection on the alternator? Then whats the little wire in the alternator plug for?

 

[73k5blazer]

So I'm admittedly not fond of wiring issues so here goes. This is on my 78 K5. As far as I know the truck wiring is original. I went to a serpentine setup off of a 4.3 out of a newer style mini blazer. I currently have the alternator that came on it. This alternator has 1 post and 1 plug that only has 1 small wire coming out of it. I guess I'm wondering where I need to go with my existing wires? Would the 2 wire from the trucks flat plug and the single wire with the rubber boot all go onto the post connection on the alternator? Then whats the little wire in the alternator plug for?View attachment 212158 View attachment 212160 View attachment 212161

Find the wire in your old harness that is on (12v) when the key switch is on/run position. Splice that into your new alternator wire.

That would be my edumacated guess. I might guess there's more wires in that new alternator connector and someone pulled them out, or someone's cut off the ones they don't need for whatever that came from as I know of no factory 1 wire setup.
I'd try switched 12v to that new alternator wire and see if that makes your alt put's out 14v when spinning.

 

[broflow]

Find the wire in your old harness that is on (12v) when the key switch is on/run position. Splice that into your new alternator wire.

That would be my edumacated guess. I might guess there's more wires in that new alternator connector and someone pulled them out, or someone's cut off the ones they don't need for whatever that came from as I know of no factory 1 wire setup.
I'd try switched 12v to that new alternator wire and see if that makes your alt put's out 14v when spinning.

I'm just wondering what the 2 in the original flat plug and the other single original wire trace back to? It looks like 1 terminates into the junction block on the firewall (see pictures) the other 2 go back thru the firewall to the fuse box. I guess I need to pull the wire loom apart and see which is which?
I'm not real familiar with the function of the alternator other than it charges the battery but why would it need 3 wires? 1 to charge battery, is one a ground? Then what's the 3rd?

 

[73k5blazer]

I'm just wondering what the 2 in the original flat plug and the other single original wire trace back to? It looks like 1 terminates into the junction block on the firewall (see pictures) the other 2 go back thru the firewall to the fuse box. I guess I need to pull the wire loom apart and see which is which?
I'm not real familiar with the function of the alternator other than it charges the battery but why would it need 3 wires? 1 to charge battery, is one a ground? Then what's the 3rd?

3 and 4 are signals to a computer to tell it if the thing is on and what voltage its putting out. 1 12v wire is all you need to energize the regulator and make it put out while spinning. The 2nd wire on your truck harness....i do t remember what that was for. There was a nice website I think it was called "the 12 volt" or something that explained various alternator setups

 

[diesel4me]

The old 3 wire alternators (10SI) had 12V at both of the wires on the plug while the engine was running--one of them,usually a tan ,brown or white wire,only gets power from the ignition in the "on" position..this energizes the field windings and allows it to start charging..

The red wire on the plug goes to a constant hot 12V source,the wire(s) at the starter solenoid with the fusible links most commonly..this wire "senses" the battery's state of charge,and is what determines how much the regulator will put out...

The thick red wire on the stud at the rear of the alternator is also constantly hot and also goes to the fusible link wires at the starter solenoid..

When you go to put a later style alternator on a square body,you'll need to find out which model you have(probably a CS-130 or a CS 144 ) and google for instructions on how to wire it up--type in "10SI to CS-130 conversion" as an example,and several sites with how to instructions will appear..

 

[broflow]

I'm just wondering what the 2 in the original flat plug and the other single original wire trace back to? It looks like 1 terminates into the junction block on the firewall (see pictures) the other 2 go back thru the firewall to the fuse box. I guess I need to pull the wire loom apart and see which is which?
I'm not real familiar with the function of the alternator other than it charges the battery but why would it need 3 wires? 1 to charge battery, is one a ground? Then what's the 3rd?

3 and 4 are signals to a computer to tell it if the thing is on and what voltage its putting out. 1 12v wire is all you need to energize the regulator and make it put out while spinning. The 2nd wire on your truck harness....i do t remember what that was for. There was a nice website I think it was called "the 12 volt" or something that explained various alternator setups

Your talking the wires that should be in this plug in the new alternator off the 4.3?

The old 3 wire alternators (10SI) had 12V at both of the wires on the plug while the engine was running--one of them,usually a tan ,brown or white wire,only gets power from the ignition in the "on" position..this energizes the field windings and allows it to start charging..

The red wire on the plug goes to a constant hot 12V source,the wire(s) at the starter solenoid with the fusible links most commonly..this wire "senses" the battery's state of charge,and is what determines how much the regulator will put out...

The thick red wire on the stud at the rear of the alternator is also constantly hot and also goes to the fusible link wires at the starter solenoid..

When you go to put a later style alternator on a square body,you'll need to find out which model you have(probably a CS-130 or a CS 144 ) and google for instructions on how to wire it up--type in "10SI to CS-130 conversion" as an example,and several sites with how to instructions will appear..

Thank you very much guys that will help. It's making more sense already.