For anyone undertaking an LS1 engine swap or working on related projects, setting up a reliable fuse block and OBD2 diagnostic port is crucial. This guide provides a step-by-step walkthrough on how to build your own custom fuse block and wire an OBD2 port, compatible with LS1, Vortec truck engines, and similar setups. This ensures proper circuit protection and easy access for diagnostics, essential for tuning and troubleshooting your engine.
Parts You’ll Need
Before starting, gather all the necessary components. Here’s a comprehensive parts list for building both the fuse block and OBD2 diagnostic port:
OBD2 Diagnostic Port Parts
| Part | Vendor | Part# | Qty Needed |
|---|---|---|---|
| OBD2 Port Plastic Connector, 16 Pin | Mouser | 829-12110250 | 1 |
| Terminals – for OBD2 port | Mouser | 829-12129373 | 4 |
| Terminal Lock – secures terminals | Mouser | 829-12160437 | 2 |
| Lamp (for check engine light) | Allelectronics | check lamps/indicators, inventory changes | 1 |
Fuse Block & Relays
| Part | Vendor | Part# | Qty Needed |
|---|---|---|---|
| Fuse Block Housing kit (terminals included) | RockAuto / AUTOZONE | 85668 | 1 |
| Relay Socket | Allelectronics | SRLY-2 | 2 |
| Relay 30 Amp | Allelectronics | RLY-351 | 2 |
| Relay Terminal 14-18 AWG | Mouser | 571-42238-2 | 8 |
Note: The Dorman fuse block part #85668 is available at both RockAuto and AUTOZONE, often at competitive prices.
Fuse Block Wiring: Step-by-Step
Let’s dive into assembling the fuse block. Follow these steps for a robust and functional setup.
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Prepare the Relay Sockets: The relay sockets from Allelectronics come with pre-installed short wires and terminals. It’s recommended to remove these as they are often inadequate for the current demands of a fuse block. Use a small screwdriver to gently bend the terminal tab inside the socket and pull the wires out. Discard these wires and use new, higher-quality terminals.
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Crimp and Solder Terminals: For all connections, especially in automotive applications, crimping and soldering provide the most reliable and durable connection. Ensure you have extra terminals on hand for practice or in case of mistakes during crimping.
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Bussing Fuse Terminals: The fuse block kit includes bussed terminals. Separate a set of four bussed terminals into a group of three and a single terminal as shown in the image below. This configuration allows for both constant and key-switched power distribution.
Alt Text: Components for fuse block assembly including fuse block housing, terminals, relay sockets, and relays.
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Install Heavy Gauge Terminals: Crimp and solder heavy gauge terminals onto your main power wires as shown. These will handle the higher current input to the fuse block.
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Relay Output and Bussed Fuse Terminals: Install a heavy gauge terminal into the relay OUTPUT leg. Then, insert the set of three bussed fuse terminals into the fuse block housing as depicted. Ensure they seat properly with a click.
Alt Text: Close-up of fuse block assembly showing relay output terminal and bussed fuse terminals being inserted into the housing.
- Relay and Fuse Terminal Seating: Push the relay terminal and the bussed fuse terminals firmly into their designated slots in the fuse block until you hear and feel them click into place, ensuring a secure connection.
Alt Text: Fuse block with relay and bussed fuse terminals fully seated and locked in position within the housing.
- Install Relay Input Terminal: Next, install the relay INPUT terminal. The red wire connected to this terminal will be your main 12V+ battery power source. This wire also provides constant power to the dedicated fuse at the end of the block.
Alt Text: Wiring of the fuse block input terminal with red wire connected to battery positive for constant power supply.
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Fuel Pump Relay Wiring: Connect the gray 16 AWG wire with a terminal to the OUTPUT leg of the fuel pump relay socket. For the other relay, connect the PINK wire terminal to the relay coil location. This pink wire will be your “key hot” power source, activating the relay and supplying power to the three bussed fuses when the ignition is on.
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Key Hot Fuse Grouping: With the remaining fuse and relay terminals, begin grouping your PINK “key hot” wires. These will supply power to circuits that are only active when the ignition is switched on.
Alt Text: Pink wires being grouped together for connection to key-switched fuses in the fuse block, organizing ignition-dependent circuits.
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Install Key Hot Wires and Check Engine Light: Install all the PINK “key hot” wires into the first three fuses of the block. Document your circuit assignments for easy reference later. Include a wire for the check engine light (MIL) in this group as well.
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Constant Power and Fuel Pump Relay Input: Add the ORANGE wire for constant battery power to the PCM (Powertrain Control Module) and create a jumper wire to connect to the fuel pump relay INPUT terminal.
Alt Text: Orange constant power wire connected to PCM and jumper wire to fuel pump relay input within the fuse block assembly.
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Relay Coil Grounds and Fuel Pump Relay Control: Finally, install the GROUND wires for each relay coil. Use a jumper wire to ground both relay coils. Connect the fuel pump relay control wire from the PCM to the designated relay coil terminal. The PCM provides a 12V+ signal to trigger the fuel pump relay.
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Diagnostic Port and Check Engine Light Wires: The coiled pink, orange, and black wires are for the OBD2 diagnostic port and check engine light. Make these wires approximately 6 feet long to allow for easy routing into the vehicle’s interior.
OBD2 Diagnostic Port Wiring
Wiring the OBD2 port is straightforward, and the pinout is consistent for LS1 and Vortec truck PCMs.
OBD2 Port Pinout for LS1 and Vortec Trucks:
- Pin 2: Serial Data – Connects to the PCM’s serial data output.
- Pin 4 & 5: Ground – Connect both to a reliable chassis ground. While pin 5 is often sufficient, some scan tools may require ground on pin 4 as well.
- Pin 16: 12V+ Battery – Connect to a constant 12V+ battery source.
LT1 Specific OBD2 Wiring (96-97 ONLY):
- Pin 6: Diagnostic Request/Field Output Enable
- Pin 9: UART Serial Data
Note: 1995 LT1 vehicles used an OBD2 port but were not fully OBD2 compliant. They typically used pin 9 for data, not pin 2.
OBD2 Port Assembly
Here are the components you’ll need to assemble the OBD2 port connector:
Alt Text: Parts for OBD2 port assembly including 16-pin connector, terminals, and terminal lock.
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Prepare OBD2 Port Terminals: Crimp and solder the appropriate wires to the OBD2 port terminals. Ensure you are using the correct terminals for the OBD2 connector and wire gauge.
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Insert Terminals into Connector: Refer to the OBD2 port pinout and insert the terminals into the correct pin locations within the 16-pin plastic connector.
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Secure Terminals with Lock: Once all terminals are inserted, use the terminal lock to secure them in place within the connector housing. This prevents terminals from backing out and ensures reliable connections.
Alt Text: Wiring diagram illustrating OBD2 port pin assignments, specifically showing a TAN wire at pin 9 for a 1994 LT1 car, and labels for external connections.
Note: The image shows wiring for a 1994 LT1 (TAN wire at pin 9). For OBD2 PCMs (LS1, Vortec), pin 2 will have a purple wire for serial data.
By following these steps, you can confidently build a custom fuse block and wire your OBD2 port, ensuring your LS1 or similar engine swap is properly powered and diagnostically accessible. Remember to always double-check your wiring and connections for a safe and reliable system.
