Forum » EFI Wiring Fundamentals » Internal connections

Internal connections

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals

Page 1

I've done alot of smaller motorsport wiring in the past, but now I've wired a racecar from ground up for the first time. The car has about 70-80 connectors.

I've used separate MIL connectors for engine, front chassi and trunk. The Engine, front and chassi side has been more or less easy to manufacture, because its like a tree, starting from the main connector. The only internal connection are the ground points which goes to a few sensors.

But I struggled and spent a lot of time in the main interior harness. This one connects ECU, PDM, Dash, few Relais, Keypad, clutch, break switch, DBW PEDAL and a few more. This harness has a lot of internal connections from plug to plug and splices. The layout hasn't a tree form, like the engine, front chassi and trunk harness.

I tried both, starting with wires at ecu and go to main MIL connectors or the other way arround. Both methods are difficult because wires from ecu go to several connectors and a 90deg MIL connector is difficult do do properly with service loops when you have a bunch of wires, which are already pluged in on the othet end.

I tought about using a fourth MIL connector for the Aall connectors arround the dash.

Can some of the more experienced wire guys please explain how you do such a complex harness step by step?

Add splices. I build each leg from the device / connector toward the center (PDM, ECU? typically whatever devices have the most pins)). At some point the two legs that need to be connected can be spliced.

In planning, I create a spreadsheet with a section for each connector, and length of wire from that connector to where it is connected / spliced.

Sorry that's not step by step, but I can't so that in a forum post.

G'day Adrian.

The way I approach any motorsport harness build is with a lot of planning. The planning probably takes more time than the actual construction! Sounds like you've got the design sorted as far as where every wires makes its connections, are you trying to build the harness in the vehicle, or following a diagram on the bench? For complicated harnesses, building them in the vehicle is more trouble than its worth.

You want to make a mockup of the harness using nylon rope or something similar, so you know where all your branch points and connectors need to be. You can then follow this out on the bench.

Create a document that lists every harness section, so this will be every section of harness that ends in a connector, along with every section of harness that spans between two branch points. As you know where all your wires are going, you now also know the exact wires that will be in every harness section. List these in your document under the harness sections, and you'll be able to plan where the wires lie in your concentric twist.

Use connectors boots, and sealed branch points as locations where you can splice wires, as the rigid boots at these points give great strain relief. These points are also the locations where wires can transition from one layer to another to keep things tidy.

For the actual construction, give this facebook post I made a few months a go a read:

It outlines where I try and start the construction process.

Hope that's helpful, let us know how you get on!