Below is a good example of how to keep it neat. This builder made a tray to load all the wiring into including those wires that are not needed.

Make sure that all connections are clean and tight and that they are secured properly ensuring no cables can contact moving or hot parts and that rubber lined P clips or plastic ones are used. If cables pass through an alloy panel then you should use a proper grommet to protect the cable. P clips should be a maximum of 200mm apart.

The MX5 loom for the headlight wires are too long for the driver’s side and will need reducing but the passenger side wires are about right including horn and fan and can be kept tidy.

If you have a MKI donor then it has separate side/indicator units so a slight loom mod is required here to connect to the MEV headlights with indicators and side lights all in one unit.

The battery can be mounted behind the seats and a box made to protect it. Not an IVA requirement.

A wiring tray is available from MEV that makes it easier to install the electronics.

The fog light needs to be only lit when the dipped beam, main beam or front fogs are lit. The rear fogs may continue to work until the other lights are switched off and then they must remain off until switched on again, this is to stop people accidently leaving the fog lamps on. This is an IVA requirement since 2013

If you are using an early donor, you will need additional wiring, CBS sell a controller that will help you - here

You can save a lot of complexity in the wiring loom and thin this out substantially. This makes it easier to install and maintain. This step is 100% not necessary.

The common advice is to use the wiring diagrams to find out what cables you need to remove. It is best to de-pin these completely from the connectors rather than simply cutting them. You need to take care as often the wires will have multiple splices in the loom from the factory, so make sure you trace the wires full length before making any cuts or removing. Some will be obvious (like heated seats, power windows etc) and others will take more studying before removal, this generally goes with how confident you are with wiring. After each wire is removed it's recommended to test all functions on the car so that if a problem does occur it's easy to troubleshoot.

If you are stripping the wiring loom back to a bare minimum it is worth noting that you generally don't need to touch the engine bay sub-harness as there is very little to remove here. The majority of wiring to remove is in the middle “dash” harness, and the rear harness.

You can see a few photos here of the thinning process and the amount that it removes.

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