Hey everyone, I'm new to this forum as I had recently purchased a 95 S10 Blazer. It's a 4 door, 4x4, auto SUV. VIN is1GNDT13W7SK22007. I am having trouble keeping the battery charged. I had taken it to Advance Auto to have them check the charging and there was NO recharge to the battery. I then took the vehicle home, purchased a new alternator removed my old one and went to Advance. Had them test alternator to make sure it was actually bad and turns out it was fine. I checked the connections to the alternator and the clip with two(2) wires actually had one wire just hanging there. The two wires are colored BROWN and RED. The BROWN wire was connected but had been spliced. The RED wire was just sitting there so I looked where the brown wire was coming from the harness but I cannot find the RED wire. I took it to a mechanic and he was also unable to find the wire. So I am wondering whether or not it is suppose to be wired to the harness. If it is then I'm hoping someone may know how I can rewire it. I have read that the wire comes from the ECU/PCM which is what tells the alternator to charge the battery. Maybe someone can tell me what pin this is and how to wire the RED wire to the alternator because I believe it may need a resistor or something to keep from blowing the voltage regulator within the alternator. Thanks to anyone that can help!!!

 

Okay.. just because I'm a nice guy I spent 20 minutes confirming what I already sorta knew.
Pretty damn sure the ECM does not control the alternator in this series.. that came later.


If you only have two wires to your alternator, the brown one connects through the Inst cluster 'alternator' light to 12 volts.

The RED heavy gauge wire is supposed to connect through a BLUE (12 ga) fuselink directly to the positive battery terminal, which you should find has three red wires from the post connector.

One red wire to starter, one to the underhood fuse block, and the third to the alternator.

I bet you can find it now...

If that battery terminal doesnt have it either, that would be weird. What I expect happened is either the fuse link blew or someone stole it to use somewhere else.

 

Yep, big red one goes right to the batt. (at least on mine it does)

 

I had previously posted a reply with pictures but I guess was never approved but I'm sorry, it's not the red wire going to the battery. That wire is on the back of the alternator connected on a post with a nut that tightens it down. I see brown wire as well but the wires I am talking about are connected onto the back of the alternator with a connector that clips into it much like how the radio harness connects into the back of a radio. On my connector there are 2 wires coming out, I'm not sure if only one was necessary for the alternator and the previous owner had just replaced it with a 2 wire and had left the red wire hanging there but the alternator is not recharging battery so I'm pretty sure it has something to do with it. The battery gauge works inside but slowly looses charge and never really goes above 9. I will check fusible link just to make sure everything is correct but last time I checked with Volt-Ohm meter it had full power.


PICTURES WORK!! Here is what I was talking about. The connector as well as wires coming out of it. As you can see the red wire isn't connected to anything. Thanks!!

 

You need the red wire connected...this is the voltage to the coils in the alternator. Somewhere you will find the other end of that red wire. Previous owner must have spliced in a new connector.

This is why the alternator is not charging the battery.

 

I would love to help out on finding the wire but it's 10* this morning and nothing starts my day off worse than frozen fingers.

However 1 of the wires is for the gauge. The other is the voltage reference.


Sorry for the large picture. Without the refrence the regulator does not know how much to put out so no charging will be done. Judging by this you should be ableto check the voltage at that wire with the ignition off. If you do not have 12V there, you need to put 12V to the red wire. Verify that splice is good as well. Would hate to have that be the issue the whole time.

 

I know I'm asking for a lot but I have been unable to find the wire from the harness that would connect to the red one. I had opened up the loom and went from the front of the engine, along the driverside then all the way to the back of the engine and still cannot find the wire. Again, I may be asking a lot but was hoping someone might know where the wire comes directly from that I can hardwire it and just run one from "A-B" then I wouldn't have to rip apart the whole harness to find it. Thanks for any help!

 

You should have one large red wire to the battery on the large post at the back of the alternator. There should only be one other wire (brown) in the 4-pin connector at the back of the alternator. The brown wire should show battery voltage (or very close to that) when the key is on.

*EDIT* - I had to go on my phone to view the pictures. It looks like someone swapped alternators at some point & changed the connector. Maybe they have the wrong wire attached.

This is common if your truck came with the CS130 which wasn't all that great and barely could attain 105A while the higher output CS144 was capable of higher than its rated 125-145A (depending on construction) in most cases. Since the wiring is cut up on your truck, that is what I think has happened. Most references on the net concerning the CS130 to CS144 swap state that the 'S' terminal (the larger hole in the connector you show) needs to be looped back to the +B post (large red wire) on the alternator for a voltage reference. Also, the brown wire needs to have between 35ohm & 350ohm resistance from the terminal in the connector to the positive post on the battery with the ignition on. If the resistance is too low, the alternator will not work correctly. If the charge indicator light in the dash is blown, the circuit will read open (infinite resistance) and will not have +12V with the ignition on. Which terminal you use though depends on whether your truck has a charge lamp (which it should).

 

Sorry, i just reread your response. So what you are saying to do is connect a wire from S terminal directly to battery and I should test resistance in L terminal to battery positive to ensure it's between 35ohms and 350 ohms?? If so then what gauge wire should I use to connect from S to battery?? Should I just connect S to post on back post of alternator or best if connected to battery to prevent any voltage drop?? Also, the other wire on the connecter will not be connected to anything?? Thanks a lot

 

The first thing I would do is make sure you have gotten the L/F terminal wired correctly by determining if you have a charge indicator light or not. You need to test the wire that is currently connected for resistance to battery positive with the ignition on. If the resistance is below spec, this wire needs to be connected to the L terminal (middle terminal of the smaller spades in the alternator). If the resistance is within spec, then the wire should be on the F terminal (smaller spade closest to the large spade). If it's open, you have a problem with the circuit that needs to be diagnosed and fixed before proceeding.

The wiring in your current plug does not have a female terminal in the S location. The two wires currently in there correspond with the L & F terminals in the alternator. I would see what happens if you find that the currently connected wire is on the incorrect terminal after testing the resistance and connect it properly before attempting to connect the S terminal.

If it comes to it, use a 10ga wire to connect the S terminal to the battery post. You'll need to get the appropriate terminal for the wire or just buy a new plug that comes with 4 wires already in it (AC Delco # PT2297).