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Thread: LS1 PCM wiring

  1. #1
    Registered Member WagonCrazy's Avatar
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    LS1 PCM wiring

    I'm in wiring jail tonight...

    Anyone know where the brown-with-red-stripe wire goes? it's the last one to wire up and now I have to get under the Nomad to figure out what wire that's for...(comes thru the firewall from the engine compartment somewhere).

    IMG_3786.jpg

    IMG_3787.jpg
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  2. #2
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    By the label on your PCM it says it's flashed and pinned as an 02 Camaro which is very common. Looking at the pin outs for an 02 doesn't show them having a brown with red stripe wire, what was the wire harness originally from? If you can tell me that I probably can tell you where it would then land for the 02 Camaro PCM connector.

  3. #3
    Registered Member WagonCrazy's Avatar
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    Thanks Bluegrass. I sort of posted that more or less sarcastically last night. I've got the pinout diagram from LT1swap and have everything else accounted for. But this one wire is not called out for the PCM (by its color...as you correctly mentioned) and it was put in by a previous owner prior to me doing this whole swap, and it went to pin 85 of a relay. I just need to jack up the car and get under it and see what this wire goes to in the engine compartment, then figure it out.

    I started with a previous owners attempt at rewiring for this LS1, and then ripped it all out, changed the location of the PCM and EZWiring fuse panel, added more relays, circuit breakers,etc.
    So kind of started over with the wiring and am figuring every circuit out....one by one...so that I understand what I'm doing.

    It's a mental thing (wiring in general). Mostly not to get distracted with ANYTHING ELSE while I'm working on it...so that I don't screw something up due to distraction (which is the primary cause of my follies). All is well here in SoCal though...just want to get this Nomad to a point of starting it up SOON.
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

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    Quote Originally Posted by WagonCrazy View Post
    Thanks Bluegrass. I sort of posted that more or less sarcastically last night. I've got the pinout diagram from LT1swap and have everything else accounted for. But this one wire is not called out for the PCM (by its color...as you correctly mentioned) and it was put in by a previous owner prior to me doing this whole swap, and it went to pin 85 of a relay. I just need to jack up the car and get under it and see what this wire goes to in the engine compartment, then figure it out.

    I started with a previous owners attempt at rewiring for this LS1, and then ripped it all out, changed the location of the PCM and EZWiring fuse panel, added more relays, circuit breakers,etc.
    So kind of started over with the wiring and am figuring every circuit out....one by one...so that I understand what I'm doing.

    It's a mental thing (wiring in general). Mostly not to get distracted with ANYTHING ELSE while I'm working on it...so that I don't screw something up due to distraction (which is the primary cause of my follies). All is well here in SoCal though...just want to get this Nomad to a point of starting it up SOON.
    Gotcha I feel your pain. No fun to follow someone else on that kid of thing!

  5. #5
    Registered Member WagonCrazy's Avatar
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    Turns out, that brown-with-red-stripe wire goes to a Backup Light switch mounted within the T56 transmission. That switch has 2 wires coming out of it...both are brown-with-red-stripe in color. One of them is cut short and has a connector set up for grounding it to the transmission case.

    IMG_3795.jpg

    So that means the previous owner intended to have the backup lights operating via a "ground" signal to a relay. (Which is why the other end of that wire was label as pin 86 on a relay)
    So I drew out what I determined would be the appropriate circuit design, then tested this by hooking up the wires to a 12 v source and it worked as planned...( with the actual backup light switch throwing a ground signal at the relay to activate the lights).
    Simple diagram for anyone who wants to know...

    IMG_3796.jpg
    1957 Nomad- LS1/T56 on C4 chassis
    1959 Fleetside Apache 1/2 ton, shortbed, big window, 327ci.

  6. #6
    Registered Member chevynut's Avatar
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    You don't need a relay for the BU lights, and I wouldn't use one myself. I'd just switch the 12V with the BU light switch. A lot simpler, fewer parts. Just run the "ground" wire to a fuse (switched 12V), and the other brown/red wire to the backup light wire.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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    Quote Originally Posted by chevynut View Post
    You don't need a relay for the BU lights, and I wouldn't use one myself. I'd just switch the 12V with the BU light switch. A lot simpler, fewer parts. Just run the "ground" wire to a fuse (switched 12V), and the other brown/red wire to the backup light wire.
    Only if the switch is rated for the back-up lamp current, which if not the relay can handle the power for sure.

  8. #8
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    Only if the switch is rated for the back-up lamp current, which if not the relay can handle the power for sure.
    Just about any switch can handle the miniscule current of a pair of backup lights. The 1073 bulb used for stock backup lights are only about 23 watts, or 2 amps apiece for 4 amps total. Surely the T56 switch can handle that. And if using LED bulbs it's about 1/10 of that.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  9. #9
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    Quote Originally Posted by chevynut View Post
    Just about any switch can handle the miniscule current of a pair of backup lights. The 1073 bulb used for stock backup lights are only about 23 watts, or 2 amps apiece for 4 amps total. Surely the T56 switch can handle that. And if using LED bulbs it's about 1/10 of that.
    So I'm guessing your car doesn't have, or need any relays, and you just run big wires, and switches to every device?

  10. #10
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Rescue Dog View Post
    So I'm guessing your car doesn't have, or need any relays, and you just run big wires, and switches to every device?
    There you go again with your BS. Did I say you never need a relay? No, I didn't, but as usual you try to twist and distort what people say and put words in their mouths. I have relays where I NEED them.

    So I'm guessing your car has relays everywhere, even where they're not needed and you just run small wires and use relays for every device?

    You don't need a relay when the load is small and a switch can handle it. You use relays where you NEED them, either for logic functions (such as AND/OR) or to carry high loads. The backup light switch on a T56 is meant to break the circuit to the backup lights, not to run a relay. That's how it's wired on cars that have them because the load is small and the switch can handle the current. And with LED lights you surely don't need a relay.

    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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