how to wire alternator- ls1 pcm with 05tahoe 5.3 engine - Forums

how to wire alternator- ls1 pcm with 05tahoe 5.3 engine

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Old 02-14-2013, 12:54 PM   #1
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Default how to wire alternator- ls1 pcm with 05tahoe 5.3 engine

the motor and harness is from an 05 tahoe. the pcm is an ls1 from the early 2000's. i bought the car 3 weeks ago and finaly got it tagged and insured. went to drive it last night. and the battery was dead. no problem, i jump started it and it was running fine. took the cables off and got in. it started to idle up and down and finaly died. went to crank it back over and it didnt have enough power to click the solenoid. jump started it agian. and left the cables attahed to help charge the battery. after 5 minutes i took the jumper cables off. got inside and held it around 2000rpm to let it charge. eventually the same thing happened, it idled rough then died and couldnt click the solenoid..

pushed the car back in the garage, took the battery out and hooked it up to charge. i then looked at the connection at the alternator to figure out why it wasnt charging and keeping the motor running. the pigtail has 2 wires coming out. but one of them has been cut at the pigtail and the wire was either removed or pulled some where else and connected to somthing. i was to pissed to keep tracking it down. I have had nothing but electrical problems since i got the car home so after this i was done and went inside.

i dont know which wire was cut i didnt look at the colors. i have been comparing the wiring diagrams for both an ls1 and an 05 tahoe but i dont know what i need to do to enable the pcm to control when the alternator is charging.

the ls1 uses one wire to activate the alternator at pin 15. the rest is controled through the IPC and then a signal is sent to the pcm
the tahoe pcm uses pin 15 as generator regulator control and pin 75 generator field duty cycle signal.

would the charge indiator control just be battery 12v reference and then the generator field duty cycle control would be key on?? this is just my guess, im going insane trying to fix all the wiring problems.

i just dont know how to wire this properly. any advice would be appreciated.
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Old 02-14-2013, 02:10 PM   #2
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Have you taken the alt to be tested? Having it tested would be a great place to start. Early 2000s PCM only uses one wire, the pcm nor alt care that you are running a 5.3 eng harness.
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Old 02-14-2013, 09:18 PM   #3
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found my problem. well both of them. not only was one wire removed from the harness, but the wire to the pcm to enable the alternator was also removed from the pcm, the pin cut off, and the wire was spliced to another wire that went no where. i gues when the original builder was modifying the harness he forget to finish wiring the alternator. maybe that explains the brand new battery and the new alternator.... doesnt explain how he has supposedly been driving the car for months without problem... guess he stretched the truth a bit.

i am splicing the wire from the alternator back to pin 15 in the pcm which is the command signal for the alternator to start charging. i hope this will fix my problem and then its on to the next problem that is sure to show up unexpectedly.
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