Engine Wiring Harness: add-on or replacement?

[debrucer]

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?

 

[debrucer]

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!

 

[debrucer]

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

 

[plaaya69]

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.

 

[debrucer]

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.

Six years later and here I am back in this thread . It would have probably been a good idea to understand the “why” of the following:

“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.”

My stand-alone ECU does not have inputs for a lot of stock components. By thinking (and saying) that I was returning the setup to OEM before modding to the Speedy, or by saying I was going to build the car for ECU to be switched between OEM and after-market by unplugging one, and repluging the other, was at best, wishful thinking. At worst, exposing my lack of understanding of individual systems.

My never-ending build continues… it’s great to have SM back. Time to review a bunch of old posts. There’s a ton of information in them that will be best used by me. Custom answers to questions I’ve had over the years.

Facebook can’t f***ing do that

Welcome back SupraMania. Thanks @Jeff Lange

 

[eraezer]

In my opinion: replace.
The "Why?": First of all age, if you have some defects due to age; dry and brittle insulation, corrosion etc. it might be very hard to determine where the problem is. Another thing that many seem to overlook is the requirement set by the electronics. The easies example is the wiring for the CAS. If you simply replace the stock ECU with anything else you might run into some problems with noise etc. The stock ECU is prepared for this with built in signal processing. By adding new shielded wires and adjusting the gaps of the sensors a lot of noise is removed and if a VR conditioning circuit is added, well then you have a very nice signal to feed the cpu.

When I started on my Megasquirt installation I built a harness that was laid out in parallel with the stock harness so that I could switch between the two to avoid getting stranded.
When I was happy with the function of the MS, I removed the stock ECU and harness.

I would recommend that you skip the resistor solution for the injectors as that is basically like limiting them. If you want to use low impedance injectors, then you need a peak and hold driver. The easiest way is to use high impedance injectors, which many aftermarket injectors are.

The building of a wiring harness is basically the same for every stand alone, you need a wire going from a pin on the ECU to a pin on a sensor for example.

A good starting point is something like what diyautotune.com sells for the Megasquirt, a wire bundle without any connectors. Then you have marked and color coded wires.

just my 2 cents.

 

[debrucer]

In my opinion: replace.
The "Why?": First of all age, if you have some defects due to age; dry and brittle insulation, corrosion etc. it might be very hard to determine where the problem is. Another thing that many seem to overlook is the requirement set by the electronics. The easies example is the wiring for the CAS. If you simply replace the stock ECU with anything else you might run into some problems with noise etc. The stock ECU is prepared for this with built in signal processing. By adding new shielded wires and adjusting the gaps of the sensors a lot of noise is removed and if a VR conditioning circuit is added, well then you have a very nice signal to feed the cpu.

When I started on my Megasquirt installation I built a harness that was laid out in parallel with the stock harness so that I could switch between the two to avoid getting stranded.
When I was happy with the function of the MS, I removed the stock ECU and harness.

I would recommend that you skip the resistor solution for the injectors as that is basically like limiting them. If you want to use low impedance injectors, then you need a peak and hold driver. The easiest way is to use high impedance injectors, which many aftermarket injectors are.

The building of a wiring harness is basically the same for every stand alone, you need a wire going from a pin on the ECU to a pin on a sensor for example.

A good starting point is something like what diyautotune.com sells for the Megasquirt, a wire bundle without any connectors. Then you have marked and color coded wires.

just my 2 cents.

Your two cents much appreciated. I was responding to my own thread after six years from the original post and latest response. SM has been down for a year in that time, too. Life has gone on at SF and FB I was really poking fun at my lack of fundamental understanding what each system on the car does. Instead of learning what I can remove or not remove, I was forcing myself to put it back to OEM spec before replacing it... knowing full-well all the time that it would be replaced. There are basic incompatibilities between the OEM setup and the one required for the aftermarket requirements. My wiring harness was "custom built" by Tweak'd. The reason I use quotes is because they built it for the wrong car. There were at least five major errors in the harness. There's a thread somewhere (prolly SF) about that experience, so not repeating here. As things have progressed, where functionality of my build has no longer required a wire, it has been cut off and capped. At least the wires that remain are new wires.

Most of the core parts for my car were purchased between 2006 and 2010. Those choices were based on what I knew then and what was on the forums at that time. My RC 550 injectors are way too small for what I'm building. I planned from the beginning to build my own ECU. It wasn't until around 2014 that Josh Stewart presented his paper that started the Speeduino project. I quickly adopted the idea. Speeduino it will be.

When the time comes, I will make sure to buy high impedance injectors. In the meantime, building a resistor pack was a few hour job including figuring out what I needed and ordering. The car hasn't run in 18 years and it's getting closer. I have no justification for needing bigger injectors today. The day will come

My personal website (shown in the footer) has some write-ups. It's not really current or kept that way. I bought the domain name and figured that I might as well use it. There's one there about my interface board, between the engine bay wiring harness and the ECU.

Without the knowledge of functionality of each of the various systems on the car, you can't just pick which wires to pass through. You've got to know the "why?" << this is what I was referring to

So, thanks again for the comments and suggestions. Read and agreed that they are good ones... under some other circumstances.