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Thread: Engine Wiring Harness: add-on or replacement?

  1. #1
    Supramania Contributor
    debrucer's Avatar
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    Default Engine Wiring Harness: add-on or replacement?

    Reading about stand-alone systems in this thread only, and not very far in... having read all the stickies, a few threads by name, and the top recent posts just to see what people are doing, and I have read comments at least twice, if not three times, about "redoing" the engine harness. I am not going with a "name brand" unit, am building a Speeduino, based on Arduino micro-controller boards, and code from a private developer. Using TunerStudio, and Megalog Viewer, I become the tuner, so as for "speaking to the guy doing the tuning" for advice, in this case, I only get the answers I want to hear. (This is the way I am going though).

    I keep thinking I will only be adding wires to the existing harness, and fixing some of the crappy connections in my 30 year old harness. I have sourced 10 colors of appropriate gauge, silicone covered, stranded wire, and I plan to use the wire lacing technique that others here have talked about. I've seen it in black and in white, think I will go with the black, to keep it clean. So no covers, no tape, no tie-wraps or wire-wraps... lace.

    Trying to decide where I'm going to build-in the resistor packs for my low-resistance 550s, Almost feels like those should be under the injector clip, not some big-ass module off on the shock tower. I'm still checking that out, as I only have my RC injectors to measure today, the originals must be here around. There are only five or six exceptions to everything for this car being in this room with me... and it has been maintained that way for years. It's all here, so I will eventually check to see if the original injectors were low or high impedance, and if low, that means I should have the resistor pack(s?) here, too.

    I have intentionally tried not to "eliminate" anything from the car/system/build, just for the sake of making it cleaner. Obviously, a whole new harness from the stand-alone on into the engine bay would be cleaner. I'm not against chucking features, if the features aren't needed... not trying either to necessarily make it street legal, and I suspect it will always be an issue getting things past California SMOG testing. Some "features" get scrapped 'cuz they're not available. Speeduino does not support "full sequential" injection, and that seems to be something people want. I haven't figured out exactly what it is though... and only thrown it out because it's not available with Speeduino. I see the add-on board that MS sells to implement that, and launch control, so maybe it's possible with Speeduino with hardware and code. (it's not the result, it's the journey)

    The Question, you ask?

    With a stand-alone, what wires REALLY pass through the firewall and to where? (okay, not specifically, but, what or how much from the original, remains?)

    When you install, say, an MS3 Pro in your Mk3 Supra, do you use anything from the original engine bay harness?
    My blog http://ToyotaSupraTurbo.com << under development and coming soon

    David Russell
    San Diego CA

  2. #2
    Supramania Contributor
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    Default Re: Engine Wiring Harness: add-on or replacement?

    There isn't a better way to get something done than to just do it... sometimes. I'm not sure this is that time. Some amount of logic says that wires used for their original purpose, can be reused, for the same or equivalent purpose. There's also some login that says "if the ECU is gone... none of the wires going to it will be needed". My original plan was to identify/inspect/repair or replace, every wire, and make what was there work, without adding too many new wires. Now I'm seeing one of those 8' universal harness, laced into the original wire bundle. Going that far allows some slack, leeway for placement of the stand-alone.

    The issue with the Speedruno not supporting sequential is being addressed with a daughter board, perhaps that's how it has to be done. That's how MS Pro3 does it. I'm not opposed. I will build that as required. The guy writing the code is fully away that people what to eliminate that extra spark

    I would still like to see some finished, fully function but customized engine bay harnesses, just to know what I'm shooting for.

    Cheers!
    My blog http://ToyotaSupraTurbo.com << under development and coming soon

    David Russell
    San Diego CA

  3. #3
    Supramania Contributor
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    Default Re: Engine Wiring Harness: add-on or replacement?

    No body responded to any questions in this thread, and I can understand why. If you haven't been through it, you will have to figure it out for the first time. Replacing the factory ECU with something made from bare boards is not anything like plugging up the stock stuff. I suspect it's not anything like wiring a Mega Squirt either. My wiring harness is still virgin. I have not started cutting wires yet. I received some advice to keep all the old there, and re-use wires in the harness, or add a minimum number. Sorry. That's not going to happen. I want new wires. This thing is too valuable to burn. I am replacing the ECU, not by-passing, not adding on. Virtually none of that crap under the hood will remain. I will add resistors to the injectors, so the resistor pack attached to the harness won't be necessary. When you cut the wires to the ECU, there are wires that must remain for the AC control panel. That gets a bit hard to mock-up, as one connector is on the engine harness, the second connector is on the fire-wall harness behind the dash (i.e., specifically, not attached to the dash harness). Then there's ABS. I have eerie feelings about ABS working. The Speeduino (uses an Arduino Mega 2560) doesn't use the stock sensors, so aside from the injector clips, there's nothing much needed on the existing harness. It comes out. There are "wheels" to be made, at least one, unless I get sexy and do something with the cams, or, I don't know. I've been learning about sensors and scopes and signal generators, and I have accumulated a lot of parts, power supplies, pieces, etc. Hooked up on Slack with others doing "Speedy". Motivated to be doing lots of little things on the car. The RasPi dash with three 7" touch screens in the gauge cluster, and another on the head unit, bought a 3700 watt amp to drive the Focal CA-100 4" speakers. All the wires have to go in after the anti-sub belts anchors are welded to the floor, and then the interior. Checked all the interior pieces the other day, nothing in need of dye (paint), one cracked item that I will get some epoxy on... but ,it all seems to be there. Head unit fits console perfectly with factory (original?) brackets. I still have one job to do on the heater/vent/ac controls down near the firewall on the driver's side. I have no real idea as to what this is doing, or how it needs to be routed. Hoping for not removing the heater box again

    I keep telling myself, it's the journey, but it sure is nice seeing some things come together.

    I shared these videos for another thread, but, here, again:

    2-min walk-around-supra.MOV (file://MYDELL-17R5720/Users/David%20Russell/iCloudDrive/2-min%20walk-around-supra.MOV)

    4-min walk-around-shop.MOV (file://MYDELL-17R5720/Users/David%20Russell/iCloudDrive/4-min%20walk-around-shop.MOV)

    They don't seem to have active links here, but, insert all between the parenthesis in your browser, and the file will download to your device.

    If you're in San Diego, Come see me! I'm here all the time

    David
    My blog http://ToyotaSupraTurbo.com << under development and coming soon

    David Russell
    San Diego CA

  4. #4
    87T Supra
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    Default Re: Engine Wiring Harness: add-on or replacement?

    I am going to be rebuilding my engine harness soon for my ECU Masters standalone and 1200cc precision injectors. I ordered 2 100 ft coleman cable 18 gauge wire spools, a few other different gauge sizes in smaller feet such as for the starter and alternator and what ever new connectors I can get my hands on from Yotaconnectors.com.

    Some things I will be deleting on the harness to clean it up a bit are the heater VSV, alarm horn on firewall, both VSV connectors under intake manifold. AFM signal wires and use the 2 temp wires for a GM air intake temp sensor.

    I don't really hear too much going on with people rebuilding engine harnesses as most of them will need them by now with those brittle wires. I know Dr tweak still rebuilds 7m harnesses also if you do not decide to do it yourself.
    2004 Lexus GS300 - daily diver
    1987 Toyota Supra Turbo - burgundy exterior w/gray interior the summer driver.
    1987 Toyota Supra Turbo - parted put
    1987 Toyota Supra N/A - Sold

    Some Pictures.
    http://www.supramania.com/forums/showthread.php?t=81005


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