Lots of companies offer loom assembly service a favorite being the Rear Engine Lucas UniLoom from Premier Wiring Systems. No loom will be specific to your car and will need adapting during the installation, not as daunting as it might sound. Basically the battery supplies power from the positive(+) terminal to the fuse box and from there to the switches; when activated these feed the component which is earthed to the chassis which in turn is connected to the negative (-) terminal back on the battery. The exception to this is the starter motor which does not have a fuse and because it draws a significant load from the battery requires a much heavier wire than all of the others. For this reason it is important to have the heavy battery negative lead bolted directly to the engine or box.

The battery power is replenished by the alternator when the engine is running and once again because of a heavier load this wire and the one from the battery to the fuse box is slightly larger. Some components are switched by means of a relay; a relay is a switch, it has the fused power in one side and the output to the component on the other or alternatively earth one side and earth line from the component the other. To connect these a bar is activated by an electro magnet energised by a low current power from the dash switch, the reason for this added complication is that some dashboard switches are unable to cope with the load requirement of the component. Other instances are the fuel pump, which for safety reasons is switched by the ECU. Power and earth for the ECU should come directly from the battery. ECU power should be switched by a relay with an inline 20 amp fuse.

With all this in mind for such a simple loom it is not out of the question to design your own loom using the Fiesta to supply the majority of wires. It is wise to purchase some crimp on spade and ring terminals (Premier Wiring Systems supply a crimping tool with their loom) and some multiplugs in order to do a neat job.

The first part of the loom to install is through the tunnel, as you can see from the photographs it is possible to fit a handbrake warning light switch in front of the lever and the wire to this can be patched into the loom at this time. With this in place you can finally fit the drivers side alloy panel to the tunnel. This job requires a degree of dexterity to get those front rivets in place!! The layout of the remainder of the loom will be dependent on the type of instruments and switchgear you have chosen. However if you can position the fuse box and any relays on the drivers side of the scuttle you may be able to utilise the free area on the passenger side as a stowage compartment.

The most common problem associated with the wiring is due to poor earthing. All electrical components need to be earthed to the chassis which being powder coated sometimes needs to be sanded back to bare metal to achieve a good connection; a pop rivet is not a suitable connector!

A fuel injected engine can only run if it has a ”brain” to tell the spark plugs when to fire and how much fuel it needs for a given load. The ECU (electric control unit) does this job by taking information from the throttle position sensor, temperature sensor, crank position sensor and the lambda sensor. Using a predetermined “map” it translates the information to send signals to the fuel injectors, coils (mounted on the end of the head), idle control valve (next to the throttle butterfly) and fuel pump. Clearly this is not a job for the amateur although kits are available for the brave MegaSquirt. Plenty of companies can provide the necessary ECU unit but not all can provide a plug in loom which could leave you patching your own together.

The most crucial part of your ECU is the “MAP”. This tells the coils when to spark and how much fuel to feed each cylinder. Most manufacturers have a start up map but only a rolling road session will give ultimate power and economy. Emerald have a map for the 1600 Sigma engine with the Sylva exhaust. Spend some time on the phone before committing.