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Time to build a motorsport harness

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals

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I feel i takes me much to much time to build a proper Motorsport harness. Maybe I have to less practise or it really needs so many hours.

So I was wondering how much time do you need to build a MIl spec engine harness with Raychem DR-25 incl. relays etc. ?

Any other example is welcome.

To the pro's: do you make a full drawing and wiring diagramm for every harness or do you have that in your head, which wire has to go to which terminal?

Good question! Honestly, I spend more time making pinouts, drawing up diagrams, and planning in general. The pinouts can take me a good week to week and a half for revisions, sensor additions/subtractions, splice reduction techniques, breakout planning, and a trying to find a general idea of how many wires in each concentric layer there will be. I also make 2 separate pinouts if a cannon plug is used so that way i can concentrate on each side of the harness separately. Drawing the diagrams is not too time consuming and can go faster once you have the hang of the program you use but in the beginning, drawing the connectors nicely can take some time. But yes to the last question, my pinouts are listed in order on the orientation in the actual connector also (wire side with tab facing up). Pinouts are always given to clients so the tuner can properly set up the ecu as well.

On the actual wiring side, that depends on your expertise and if you follow System 25 standards i.e. proper concentric twisting, shielding/draining, lacing, boots and boot sealing with rt-125. It's much faster, obviously, it you just shrink raychem over straight run wire. I spend another good week, with up to 4-5 hours a day, on the building of the harness. I never recommend sitting and wiring for long periods of time all at once since it can be frustrating and mistakes can happen. Granted, if you have deadlines, you have to follow those and just make sure to quadruple check everything. So a typical harness with a standalone from scratch can take me a good 2.5 to 3 weeks from exact start to finish. A repeat harness that I've done a few time would take about 4 days give or take, and a few hours a day give or take. I don't consider myself a pro, but I enjoy it and work harder to getting the title as a professional harness builder.

I should also add, this is just an example. Everyone is different, and theres always people better and can do jobs faster or slower. Complicated harnesses, for example, a VQ35 with a motec m880, E888 Expander, PDM32, C127 Dash, Knock module, DBW module, 6 EGTs, Racegrade Keypad and a Logger, is going to be slightly more longer to build than say a K20 with AEM infinity lol (by the way, i've never actually worked on a harness that complicated as I listed above haha)

I like that a proper harness can take a long time to accomplish, if it was easy, then everyone would do it ;)

i'm going to thread jack slightly instead of starting a new thread.

What computer programs help create clear wiring diagrams?

is there some where you can purchase the system 25 standards?

what tips do you have for making an "autospec" loom? little project of mine, cant justify the exhaustive cost to make a milspec loom as the car is rarely used so I don't need that degree of reliability.

Good planning software for diagrams is Microsoft Visio

Visio is perfect for basic wiring diagrams. HarnWare if you're serious and have the money.

I received my System 25 codes of practice for free with a simple email and a couple days patience. There's 58 "chapters" of them ( 1 is index) I've only gone through about 10 lol Not all apply to motorsports.

My only tip is to practice what you see. Everyone wants to find reading material for it, and there is simply not very much out there. Sure, everyone has read the RB-racing wiring page, but that is only to get an idea of it. There's so much more involvement in the real world.

I would give racespec a call, he sells DIY kits that have everything you need for certain engines i.e. Wire, connectors, terminals, splices, raychem. That way you dont have to spend the huge amounts of money in stocking huge supplies. If you're still in a budget to make an "Autospec", you would be practically using TXL wire all in 18 awg (maybe 20) mixed splices and expandable sleeving? Check out and they have bunch of stuff that should help you out. Or just go with Painless performance harness :)

Happy wiring!

Thank you for answers.

I'm also using Microsoft visio for drawing.

Do you draw every singel wire or just make the layout and a list of connections next to the connector?

As I know, there is no Visio database for plugs and devices. I made a few for my own and use them, also if in reallity there is another connector. Simply because it takes me to much time to draw every connector.

What do you guys think about a sharing database? Maybe HPH can manage it. I think anyway that a HPH could and should introduce some kind of database with things like injector lag time, camshaft specs, engine infos etc. I would also happy pay for it, if it saves me some time.

That's how we all do it. You only have to draw a specific connector once and then you can save it in the library for copy pasta :) Sure, it's time consuming. But everything about proper wiring is. Once you got all your connector drawings, and familiarize yourself with harness drawing, it doesn't take all that long to do a visio drawing. On the sharing database, what exactly are you trying to share? The things you listed are already available from the manufacturers who make them :)