harness design

I'm trying to design and build harnesses for my r53 mini, its a stripped out road car being built for time attack so I need to retain some oem functions and be able to pass a uk MOT, I've watched all the wiring courses a couple of times through and just can't help but feel like I'm missing something when trying to put down what I need incorporated in the design.

I want to be able to make a body harness, locks, lights, wipers and such and an engine/operation harness.

I just need a bit of help to understand the layout and planning as all my drawings are rubbish.

thanks

Why don't you start by looking at the factory wiring documentation (usually found in a workshop manual, or perhaps a dedicated wiring book usually available from a vehicle dealer), and just eliminate the parts you don't need / want. Then condense what is left into a form that you can use to build your harness. If I were trying to keep an existing car road legal, I would think seriously about just modify the existing harness (strip out parts not used/needed), then add motorspecific parts (ECU / dash / master switch ).

For new harnesses from scratch, I usually decide how to am going to break it up (engine harness, front chassis, cockpit, rear chassis, all this plugs into (or is part of) a core harness that probably has the battery / master switch / PDM.

I've already thinned out the oem loom and what I needed to work still did it just doesn't look good and there sections that are really messy with large bundles of wires that could be condensed.

I've got digital dash and some other bits to install and want to fit a pdm and can keyboard and steering wheel controls.

If you've cut off the excess wiring, you have a good starting point to start from scratch because you know the wire run lengths, connectors required, etc if you want to keep the same routing*. You can now plan how to integrate the new parts of the harness you need, with the renewal of the parts you need/want, to build up the complete assembly from scratch.

It can be damned confusing, so you may find it much easier to break things down to sections, such as what do you need to run to the rear, like lights, pumps, maybe the main battery routing, etc; what you will need inthe front of the vehicle to run the engine, lights, fans, etc; what you need to keep within the passenger compartment, such as ECU wiring, switch wiring, instrument and warning light wiring, etc. - then there are the things like ABS sensors and its control unit.

*You may decide to change this, though, as you may find you can run more direct routing.