HARNESS LAYOUT CONCERNS

I've just completed the course for Practical Wiring as preparation for creating a harness for my company's EFI system. I have followed the tutorial's instructions to the letter but do not think that I have designed something that is workable.

The tutorial provides a template for a "trunk" section with breakouts on either end. One end has the breakouts going to the ECU and the other to sensors, actuators and other devices. My harness layout has two branches on the ECU side - as the ECU has two connectors on it. The other end, however,has 20 breakouts from the "trunk". I'm wondering if this is going to work in reality since 20 breakouts with Raychem tubing on them is going to be a rather large bundle.

I have tried to reduce the number of branches on the component side of the harness by grouping wires that travel along the same path for a distance to share a breakout at the end of the Trunk, but I still have 20 and I'm worried that this will not appear professional if I were to proceed.

I have a CAD drawing of the layout that I would like to share with someone at HP Academy. This project is urgent so it would be nice to get a timely

response.

Thanks for your time,

John Schimenti - Director - E-Torque, LLC

John,

You can upload an image when making a forum post, so feel free to share an image of the layout if you'd like feedback from the group.

What's your specific concern with having 20 branches? Depending on the application, a complete ECU harness may go to all corners of the vehicle. Perhaps to a fuel pump in the back, wheel speed sensors at all 4 corners, various parts of the engine bay, display devices and input switches, buttons, keypads in the cabin and more, so 20 doesn't sound like a wild number.

On a V engine you'll also have separate branches per bank for things like injectors, coils, so that will increase the total count as well. As you mentioned, you can run much of the engine portion together, then branch off where it's most tidy, to allow the wires to reach their final destination. Keeping wires grouped until they need to separate for fitment helps keep the harness tidy and professional looking.

As Mike said, "20" isn't a lot for a ECU harness, depending on what is connected to it - some of the more complex, high end ECUs can easily be over 100.

On that, the components will dictate where the harness needs to run - you seem to be working on an installation kit, so don't forget to check what your supplier(s) can offer in different connector lengths, if used, such as lamdba senders, as that may aid flexability.

As for a "professional" appearance, don't stress on that. What is more important is the quality of the work, the connectors used - labelling is great, but if you can colour-code them it's even better - and how well it fits the vehicle(s), taking into account how they're run, they're long enough, but not too lang, strain/vibration relief if needed, etc.

You may also have the option of breaking the harness down to a main trunk, and a strategic "daughter harness" that connects to it, that's tailored to different vehicles' requirements.

i can say after building a new harness for my WRX. Labels are your friend. Wire colours are ok, but require very accurate documentation that you also need to keep referring to. Whereas a label is quicker to identify.

And it may seem like it will be difficult to have a single large trunk with lots of break outs, but its actually not as bad as it appears and results in a nice, neat easy to manage harness.

If you haven't done harnesses before, my top tip is leave more length than you think, then test fit before braiding and heat shrinking.

As if you have forgotten something, or something has a branch in the wrong spot, then its a pain to strip braid and heat shrink off.

I'd also at least test fit components, i built a harness, test fit only to find it every so slightly didn't fit behind the heater core anymore. Bit of head scratching and it was solvable. But i'd already wrapped and heat shrunk it by this stage, so much swearing beer drinking resulted.

For what it's worth, I'm a fan of both. For example all the injector labels have a color stripe and say injector #, where # is the cylinder number it connects to. That was you get the specific info, but can also at a glance spot all injector plugs when the harness is off the engine.

I do agree with Mike on a both is useful you need to find the balance. Even just using consistent colours for certain things. Eg using green for all the coil triggers wires from ECU, red for power, and black for ground.

This way your label in the engine harness just needs to say "Coil 3" and you don't need 1 label for each wire.

But then on the ECU side, you add a label to each coil wire to make pinning, and testing easier

If you are an auto-electrician, or do this all the time then using distinct colour for wire and function is ok, but at a club level then wire is expensive if you need to buy one roll for each wire you need. because you want different stripes for each coil or injector.

i did my whole cars harness with maybe 8 colours. It gave me enough distinction for wires by just looking and knowing what something was, eg blues were lights and temp sensors, yellow was pressure etc and combined with labels i can diagnose and identify almost anything without having to check documentation

Sorry, I wasn't clear, I meant using colour coded connectors, and/or differently shaped/pin number, connectors as a supplement to labeled wiring terminations.

It doesn't need to be anything fancy, a little paint and/or (a) ring(s), or sections, of heatshrink will work.

It just makes it much easier, and faster, to reconnect after disconnection, for whatever reason, and makes it much less likely for an error to be made - especially in poor light conditions or where access to read the label(s) is difficult.

Same principle with using colour coding, or different size, couplings with hydraulics' systems' control blocks.