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Thread: Custom LSx Harness

  1. #1
    Super Moderator dave w's Avatar
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    Custom LSx Harness

    Attached is a pic of a custom LSx Harness built by Old School EFi. Built by tape measurements, it's not a budget "cookie cut" type harness.

    Sometimes the placement of the following are important for a vehicle, requiring "Tape Measurements"
    PCM Location
    ALDL Location
    Fuse Block Location
    Acceleration Position Sensor Location
    Throttle Actuator Module (TAC) Location
    Radiator Cooling Fans Relay Location

    Also available in "Show" quality braided loom.


    dave w
    Attached Images Attached Images

  2. #2
    Fuel Injected!
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    Looks good.

    Approximately how much is a typical LS harness?

    Would you take an engine harness and build a Ls harness that integrates with it?

  3. #3
    Super Moderator dave w's Avatar
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    The approximate starting price for a custom LSx harness is about $650 (1999 - 2002 Gen III engines - LS1, LM7, L59, LQ4 & LR4).

    The term "engine harness" could be confusing, maybe "chassis wiring" is a more accurate term? Typically, wiring to / from the LSx engine / LSx computer is considered "engine harness".

    Integrating "chassis wiring" into the custom LSx harness is something that would only be done with new wire.

    Perhaps a LSx engine harness kit is an option to integrate into existing chassis wiring as a DIY project? For example, a LSx engine harness kit could include 8' pigtails for the following:
    ALT - Alternator
    CMP - Cam Position Sensor
    CKP - Crank Position Sensor
    CTS - Coolant Temperature Sensor
    Coils Packs
    IAC - Idle Air Control Motor
    IAT* - Intake Air Temperature Sensor
    Injectors
    KNK - Knock Sensors
    MAF* - Mass Air Flow Sensor
    MAP - Manifold Absolute Pressure Sensor
    TPS - Throttle Position Sensor

    * Available as a single 5 pin connector or separate 2 pin IAT connector / 3 pin MAF connector.

    dave w

  4. #4
    Fuel Injected!
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    Well, most older pre fuel-injection GM's have a separate engine harness and forward lamp harness connected at the firewall plugs behind the fuse block.

    The engine harness basically had the ignition, starter, and sensor wiring. Sometimes the alternator would be in this harness since it was easy to wire alternator to solenoid. Sometimes the heater motor was included since the heater motor was close to the starter wires and easy to just plug it in.

    The lamp harness had all the wiring for the lamps and whatever else had power on the radiator support. Sometimes the alternator would be in this harness if the harness passed close by it.


    So, make the LS harness sit on the engine nicely like you already are, but include some extra wires that enter and exist in certain spots for other functions? For example, wires for oil and coolant temp gauges or a wire for the alternator idiot light.
    Last edited by lionelhutz; 01-08-2018 at 11:12 AM.

  5. #5
    Super Moderator dave w's Avatar
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    Quote Originally Posted by lionelhutz View Post
    Well, most older pre fuel-injection GM's have a separate engine harness and forward lamp harness connected at the firewall plugs behind the fuse block.

    The engine harness basically had the ignition, starter, and sensor wiring. Sometimes the alternator would be in this harness since it was easy to wire alternator to solenoid. Sometimes the heater motor was included since the heater motor was close to the starter wires and easy to just plug it in.

    The lamp harness had all the wiring for the lamps and whatever else had power on the radiator support. Sometimes the alternator would be in this harness if the harness passed close by it.


    So, make the LS harness sit on the engine nicely like you already are, but include some extra wires that enter and exist in certain spots for other functions? For example, wires for oil and coolant temp gauges or a wire for the alternator idiot light.
    I agree, with planning a "Custom EFI Engine Harness" can incorporate "Chassis Wiring". There is somewhat of an industry standard in automotive wiring products. Most major brand name wiring harness suppliers offer chassis wiring for a specific Make / Model / Year vehicle, with an additional harness product line for a EFI conversion.

    Most of the time a custom EFI harness will be installed in a vehicle with a comfortable budget wanting a clean look with components placed in specific locations. Most of the time, a vehicle built with a comfortable budget has selected a major brand name chassis harness.

    dave w

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