Bespoke Wiring Harnesses

Simtek (UK) has been designing an manufacturing bespoke and low volue wiring harnesses since 1999.  This page describes the range of work we do and why we love doing it!  

Bespoke Wiring
Bespoke loom for R5 Evoque

Building a wiring harness - for beginners: Part 1


The wiring is usually the one thing people dread having to do, and when they do think about it, well it can only be a few wires from here to there can’t?  Just a few wires to get things going that’s all we need!

But just think about it for a little longer; is it?  What does the wiring system really do anyway?  A lot more than you might think, or at least it should...

The first thing is don’t be afraid of it and then whatever you do don’t dismiss it, if you do - you do so at your peril.  

Whatever reason you want to build or have built a harness, I am pretty certain it’s not so you can spend hours fault finding or stuck at the side of the road or even thinking I wish that worked better.

Automotive wise the wiring and electrical systems are the only parts of a car that have changed in terms of their influence on the function of a car in the past 60 Years. The Electrical system now plays a major part in a vehicle’s drivability, power delivery, economy, safety and, don’t forget, ergonomics (the nice bits were your seat warms up and your IPod connects to the radio).  Even the most hardened petrolhead secretly craves a little functionality and comfort.

If you take a little time to understand the electrical system and the regulations, not necessarily learn all about it, but just understand what it does, what it can do and what you must do, then you will start to understand what you can do, and why those tittle extras are worth the time and effort.

Designing and building or even having a harness built to your specification can be one of the most satisfying parts of the car build and the finished car, having the right function how you want them and those little extras is as satisfying as a perfect fitting chrome trim, those well-tailored seats the or that crisp sounding inlet system.

Once again don’t be afraid of the wiring break it down into easy to bitesize sections to avoid overwhelm.

When designing a harness there are 3 main things to consider: -

  • The components fitted to the car and their specifications (current draw, voltage connector pinout etc) 
  • The legal requirements you might need to comply with whether they be for IVA or a motorsport regulation
  • The location of components and routing of a harness which is especially important in a smaller or tightly packaged vehicle.

Designing a wiring harness from scratch – 1st Stage

  1. When designing a wiring harness the first thing to be done is to list every electrical component to be fitted to the vehicle; include its current draw, number of connections and expected location in the vehicle
  2. Next, draw a schematic or ‘stick’ diagram to establish the physical layout of the wiring harness.  Using string or a piece of flex, measure out the lengths of each section by using the flex as you intend to fit the loom in the vehicle, into and around the corners etc.  Apply notes to the diagram of all the measurements, angles and directions of branches.  Make notes of where rubbing or heat protection will be required. Think about your preferred method of going through a bulkhead, if required, grommet or panel-mount connector can be used. 
  3. Now you can take this information to a bespoke wiring harness specialist or DIY. 


If you DIY the next phase is to decide on the connectors:  See Part 2.