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2012 Sierra alternator help

Kyle Grasso
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Kyle Grasso Enthusiast

Kyle Grasso

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Hey guys I recently upgraded from a 2003 Silverado to a 2012 Sierra and need to upgrade my alternator for my stereo system.  I have a 4 wire high output 250a alternator from my 03 but the 12 uses the 2 wire alternator.  Is there a way I can properly hook the 4 wire up to the 2012 truck?

Kyle Grasso Enthusiast

Kyle Grasso

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Well I figured it out on my own finally.. for future reference in order to run a 4 wire alternator on an 05+ 2 wire style alternator you need a p103 trickery device from mechman alternator.  That plugs into the 2 wire alternator harness from your truck, then you get a 4 wire plug with 1 wire coming out and connect that to a switched 12v source somewhere at the underhood fuse panel preferably.  Done

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Kyle Grasso Enthusiast

Kyle Grasso

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Forgot to mention that the p103 tells the rvc system that everything is ok and normal so the battery light on dash stays off.  The 4 wire alternator will work as it always has and provide a steady 14.2-15v 

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Kyle Grasso Enthusiast

Kyle Grasso

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Its not done yet but I decided to just go with a 2 wire alternator since I found a 300a for a good price.  I hope I don't regret it but theres plenty of people out there running them with more power than I do.  I have a 12" skar audio dvc sub in their ported enclosure running off a Skar 800w rms monoblock (sub is 600w rms).  Then I squeezed a 4 channel amp under the rear seat mounted on the transmission tunnel hump thats powering the 2 front door speakers and 2 tweeters located on the dash.  This is just a temporary set-up until I have the alternator installed along with upgraded wiring.  Thats where Ive run into another hiccup with the 05+ trucks.  GM decided to install a sensor on the ground wire from the battery that monitors voltage and helps the ECU control the alternator.  If you add any grounds they must be run through this sensor or your alternator will overcharge.  Im not 100% sure yet but I think you can upgrade/add grounds as long as they dont connect directly to the battery and bypass the RVC(regulated voltage control) sensor.  My truck has the normal engine block to firewall ground thats not run through the sensor and im sure theres more somewhere.  I plan to just swap these factory location grounds out for 1/0 wire instead and keep everything attached to the same location with exception of the 1 battery neg to the front of the engine.  That wire will go directly to the alternator mounting bracket.  Now on to whats going on with the fuse located on the positive batt terminal.. never thought replacing some battery cables would require so much research! Thanks GM!

Kyle Grasso Enthusiast

Kyle Grasso

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Im closing on a new house January 6th with a 36x30 2 story garage built in 2019 out back.  It has a brand new lift and pellet stove in there with a man cave upstairs!  I figure I'll be living in there for awhile while I pull the truck apart and re wire everything.  Lmao

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