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Here I will outline building your own fuse block and attach relay sockets. This is a general guide that will work for most any wiring harness. I use this same basic setup for LT1, LS1, Vortec Trucks etc.
First off, the parts you will need to build the fuse block and OBD2 Diagnostic Port.
I have found that AUTOZONE can order you the fuse block, with terminals for $5.00 part# is 85668. This is a Dorman part. From www.rockauto.com its less then $3.00.
FUSE BLOCK WIRING
The relay sockets from allelectronics will have short wires in them, with terminals. DO NOT use these, you can insert a small screw driver in the slot on the top and bend the tab, and remove them. Order new terminals. The stock wires on these relay sockets are not up to the current needs of the fuse block. Also, these sockets are the only ones I can find, that will slide onto the side of the fuse block.
Order extra terminals incase you need to re-do something, for OBD2 port, Relay sockets, Fuse holder, etc, they are not expensive, $0.10 to $0.25 each or so. I always crimp AND solider all my connections.
Picture on the LEFT: Use about a 12 AWG wire to feed into the MAIN relay. Also use 12 AWG to connector out of MAIN relay to the linked fuse block terminals. 16 AWG will be fine to feed Fuse 4. The fuse block kit (85668) will have 4 terminals linked together. I cut one of these off, to leave 3 linked together. This will allow you to wire the fuse block for 3 "KEY HOT" fuses and 1 "HOT AT ALL TIMES" fuse. You can opt to purchase additional fuse block kits and slide them together, for however many circuits you want.
Picture on the RIGHT: This is the completed fuse block. 12v+ from a battery source feeds into the MAIN relay and to Fuse 4. FUSE 4 Feeds the PCM's BATTERY supply, and the Fuel Pump Relay. Orange wires are 12v+ BATTERY, hot at all times. When the KEY 12v+ is supplied with 12v+ from your ignition switch, the MAIN RELAY turns 'ON' and supplies power to FUSES 1,2,3. These 3 fuses can be used to power your PCM Key Hots, Fuel Injectors, Coils, Transmission, Mass Airflow Sensor, Heated Oxygen Sensors, ETC. GROUND is supplied to both relays. The PCM will supply POWER to the fuel pump. This will then turn ON the Fuel Pump Relay, and feed 12v+ to the fuel pump wire (GRAY)
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.
OBD2 LT1, 96-97 ONLY will have additional wiring to OBD2 port.
Pin 6 - Diagnostic Request/Field Output Enable
Pin 9 - UART Serial Data
1995 LT1 used an OBD2 port, but were not OBD2 vehicles. These did not have a Serial Data on Pin 2. These used pin 9.