stand alone harness alternator and tach wire voltage

Hello all , newbie here just trying to learn and find the solution to my problems . I Did a LS swap using a 2002 escalade 6.0 and ECU ,,,using a LS1 stand alone harness. I noticed something was draining my battery and I found that the one red wire going to the alternator and the white tach wire from the harness has power to them at all times , even when the car is switched off . This is what was killing my battery. im pretty sure those wires are not suppose to have power to them at all times. Is there something in the ECU that controls these wires to cut the voltage on and off to these wires ? The harness has only 4 power hook up , 2 wires from the harness go to the starter , having constant power. the other two wires comes from a key on 12volt source to operate the two relays , one controls the ECU and the other controls the fuel pump relay . I can pull the , key on 12 volt power that controls the two relays and I still have voltage going to the red wire going to alternator and the white tach wire. I was leaning toward the harness being wired wrong . I sent the harness back to the company I bought it from . The company, in turn sent me the same harness back saying they had looked it over and it had tested fine. I don't know how they tested the harness but assuming they put it on a test engine and started it up but did not check the voltage when engine was off , it would have tested fine , as my engine runs fine with the harness . So now, im leaning toward the ECU either being bad or something in the programming is keeping those wires energized at all times.
I just ordered the hp tuners MPVI2 yesterday , so I haven't looked into the programming yet, and really don't know what to look for. Any help or advice will greatly be appreciated .

Thanks

On a stock wiring diagram the only red wire going to the alternator is the battery wire. Is the red wire you are talking about going to the large terminal of the alternator or to the plug? A picture would help also if possible. The white tach wire goes from the ECM to the cluster in stock form. It could have 12 volts on it with the key on if checked with a voltmeter. If it was checked with a scope while running it would show a 12 volt square wave pulled to ground if I remember correctly. I do not think it should have 12 volts with the key off unless it is wired to a tachometer that has full time power. Is it hooked up?
Have you put an amp meter inline or an amp clamp around the positive or negative cable to verify a draw? Other methods would work but I am curious if the draw visibly changes when those wires are removed from what they are connected to.
If you have not figured this out yet I can get you more information on the tach wire by checking my car later. If you post a pic of where the red wire comes from and goes to I can likely narrow down it's job.

If your situation is like my LM7 wire harness, there are two power wires that go to the PCM and only one gets power full time to retain PCM memory "learned" items - very low current used here. The other PCM power wire is powered with the ignition system powered on by the ignition key, not full time.

Could this be your problem?

Rick

What year LS1 and alternator are you using? Here's the 2002 ESC charging system diagram. My guess is the alternator is not compatible with the 2002 ESC ECM wiring.

It’s the one red wire in the plug that has power to it at all times. Along with the white tach wire . The alternator will not charge if the plug is not plugged in . And if you leave it plugged in and don’t start the engine for a few days it will drain the battery . Unplug it from alternator and it will not kill the battery . Over the last few days , I have purchased another pcm and transferred my tune . And I still have power on both wires , so I can eliminate the pcm as the problem. I’m still leaning toward my first guess which is the harness being wired incorrectly. It’s the same one I sent back and they sent it back to me saying it checked out ok with them . I’m going to pull the harness back off tomorrow and send it back to them for a second time . And yes I have did a amp draw , that’s how I found out the wires still had power on them . I started pulling wires until the draw went away . Narrowed it down to the one red alternator plug wire and the white tach wire .

You can wire in a relay to ignition feed that will cut the connection when shut off. From your description, you have two ignition fed relays to work with. Depending on how they are wired, one the relays could be stuck on. This will save the hassle of sending the harness back and eliminate the draw. As long as the charging system operates correctly. You still haven't stated year of the vehicle that you got the swap from. Also, the actual alternator model/make to determine how it's supposed to be wired. If it's a PCM controlled PWM (pulse width modulated) alternator, you need to set up correctly. Like BlazerDave stated a pic as well as the wiring diagram you are using would be great. No telling if their harness is using all of the factory colors. Color means nothing without diagram to reference.

I found this out last night . I pulled the ALDL fuse out of the fuse box . This fuse is suppose to give the obd port 12 volt constant power . The energized alternator wire and tach wire went to zero volts . I started the engine up and everything worked like it was suppose to minus the aldl fuse pulled . My tach even started working where it had never worked before. I installed the ALDL fuse while engine was running and the tach went back to zero . I ohmed the white wire from fuse box to white wire #16 on obd port and showed good . Nothing to ground or any other wires in the fuse box . From my under standing , the white wire only provides 12 volt constant power to obd port and it should be a sraight run in the harness with nothing else mated to it . I haven’t pulled the harness apart yet to trace the wire yet . But something is definitely feeding back through it to give voltage on alternator and tach wire when obd port is energized when car is in off position.

Update problem solved !
Harness was wired wrong , I tore into the ls1 stand alone harness that I had purchased and found that the obdII port wire coming from the fuse box was tied in with the tach wire. Once I cut it from the tach wire my tach started working and no more power on wire going to alternator when car was switched off . I’m assuming the 12 volt constant hot wire was back feeding back through the pcm and running through the alternator wire when was car was off .

I was having this exact same issue and this is the only post on the internet I could find to help me. I really appreciate the fact that you posted your fix once you found it. Why did they tie in that 12v to tach!??!??!??! I thought my battery was going bad and couldn't figure out why my alternator was buzzing after key off. I owe you at least 6 beers next time you're in the San Gabriel Valley/So Cal 🍻🍻🍻🍻

I?m having exact issue. What was your fix. What wires did you cut and is there any additional connections to be made thank you

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Originally Posted by Esblind23

I was having this exact same issue and this is the only post on the internet I could find to help me. I really appreciate the fact that you posted your fix once you found it. Why did they tie in that 12v to tach!??!??!??! I thought my battery was going bad and couldn't figure out why my alternator was buzzing after key off. I owe you at least 6 beers next time you're in the San Gabriel Valley/So Cal 🍻🍻🍻🍻

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I?m having exact issue. What was your fix. What wires did you cut and is there any additional connections to be made thank you

On mine there were three white wires on the aldl fuse and it only needs one to the ob port. The other two were the tac wire which was back feeding

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Originally Posted by wht69cam

Update problem solved !
Harness was wired wrong , I tore into the ls1 stand alone harness that I had purchased and found that the obdII port wire coming from the fuse box was tied in with the tach wire. Once I cut it from the tach wire my tach started working and no more power on wire going to alternator when car was switched off . I?m assuming the 12 volt constant hot wire was back feeding back through the pcm and running through the alternator wire when was car was off .

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You should post a video or some pics of where exactly on the harness you found this wiring problem. Alot of people would be appreciated

I just made and posted a video on youtube to correct this problem. Thanks for figuring it out so i could take it a step further. Cheap chinese harnesses are wll the same. Never wired right.
Video here https://youtu.be/l3F2gsD7Icg