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OBD2 DIAGNOSTIC PORT WIRING
All OBD2 port's for LS1, Vortec Truck are the same.
Pin 2. - Serial Data - FROM the PCM.
Pin 4 & 5 - GROUND - Usually only pin 5 is needed, however some scan tools/code readers will need GROUND on pin 4 as well.
Pin 16 - 12v+ BATTERY - Power from 12v+ Battery source.
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http://www.lt1swap.com/fuseblock_obd2port.html