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It is too easy to forget how complex modern cars have become. I sometimes think of my old 100E Anglia – my first car – which was already old when I bought it from an uncle in Luton for a fiver in 1970. My model had the optional heater fitted: there was no radio, no seat belts, or reversing lights. The windscreen wipers were operated by manifold depression, which meant that when the car climbed a hill in driving rain they slowed down until they were virtually stationary, at which point you had to lift your foot off the accelerator and the wipers went crazy. But then you had to change down to second gear – there were only three forward gears – and this meant slowing down to about twenty miles an hour. By the time you reached the brow of the hill there was a long queue of exasperated drivers behind you waiting to pass.

The indicator was on the steering wheel boss, there was a lighting circuit and a start/charge/run circuit – and that was it. And it was all simple. You could diagnose a fault almost without fail because the ignition circuit consisted of two wires and five minutes prodding with a sharp nail connected to an earthed bulb could find any fault. A relay then was something that controlled the generator and if that failed it either flattened the battery or melted it.

But performance there was none. Zero to sixty in your lunch hour – and if you tried to go faster the vibration would drop all of the fillings out of your teeth, even though they were clenched with fear.

The additional equipment we have come to expect always comes with a price – and not just in sterling. Additional control motors for seats, mirrors and central locking and the switches to control them all have to be connected with relays and a mess of wiring to charge and operate them. All this adds weight and a sometimes baffling complexity.

But not any more. Fly-by-wire changed that. In the 1960’s NASA realised that the tiny movements of a joystick operated by a human was not sensitive enough to land the first Lunar Module on the moon. They had the idea of intercepting the control impulses from a joystick operated by the pilot and interpreting them by a microchip which smoothed out the motion and actually fired the engines. Without this there would not have been a giant step for mankind – just a large crater. The latest Stealth Fighter is virtually impossible to fly without a computer operating the control surfaces and the human is merely another ‘input’ to be considered. If the control computer fails, the pilot has to eject!

So what is the big deal? All right, think about this. The entire central locking system, the motors, actuators, control modules, together with the electric windows, the mirrors and the seat position motors are all linked by two wires. No, not two wires each, I mean two wires for all of them. Each module and motor has an electrical supply, of course, and an earth – but their entire operation and cooperation with everything else is controlled by two wires.

This is how it works. Behind the glove compartment there is the CCM, the central control module. This is the manager of the messages between all of the modules in the multiplex system. Two wires lead from this and are connected to all of the doors, and there is also an interface with connects this module to the alarm system. There are separate modules in both front doors, and depending on spec, in the drivers seat. When you press the remote locking key, the radio frequency signal is received and the CCM checks the validity of the signal. If accepted, the CCM checks the two front door ajar switches, and if these show closed, the CCM send a coded signal (called a message) down the control wires (why just the front doors? The rear doors have slam locks.) The locks in the doors, boot or tailgate and the fuel cover receive this signal and lock. The CCM interface then operates the alarm. If the CCM receives a second lock signal from the remote within ten seconds the interior door handles disconnect from the system – the doors are deadlocked and the interior movement sensors switch on, if fitted.

But wait – it gets better. You return to the car and press the unlock button. The RF signal is received and verified, and a coded message is then sent down control wires addressed to all of the locks. They unlock. The interface turns off the alarm and the interior sensing. If the CCM has been programmed, the CCM also sends a message to the drivers seat module which then moves the motors in the seat to its preset position for this remote and moves the mirrors to the positions stored in the CCM. The CCM also turns on the interior light.

However, you may only want to open the boot. You press the boot button on the remote. This sends a signal to the boot locking actuator, and because the address is different, the other locks ignore the message while the boot motor unlocks and switches on the boot light. The alarm is still on, and when the boot is shut it is locked again.

Clever, eh? Just think of the wiring and connections the system has saved.

And it gets even better. Top spec models have "Global Open/Closing". Not available on the remote, it operates on the key if you hold it in the door lock for a few seconds in the unlock or lock position. The CCM receives the message from the door lock, and operates the global opening, and this means opening the front windows, then the rear windows and then the Sunroof. While the key is held pressed against the stop, the opening motors will continue to operate until they are all open. But the CCM doesn’t open them all at the same time, as you would expect. Oh no, that might cause too much of a load on the circuit. The CCM opens the windows and the sunroof in stages until they are all open and it does this by sending the messages to the modules in the drivers door and the passenger door in timed phases. You can watch exactly the same thing happening in reverse when you hold the key in the Global Closing position.

The resulting wiring is much simplified. Instead of a different loom for higher spec models, the loom on all models is virtually the same. A higher specification merely means that the additional module is added and the two signal wires plugged in.

Fault diagnosis should be a doddle. The CCM stores any fault, like the failure to contact a particular module or motor during operation, in a non-volatile memory for quick retrieval by WDS. There is also a limited operation strategy which ensures safety by limiting some functions automatically if a fault may make it dangerous.

Jump-Starting a flat battery
Make no bones about it, these modules are nothing less than computers, and extreme care must be taken not to overload or flash the car electrics. If arc welding has to be done, then you must disconnect the battery before you start. Using jump leads to start the Scorpio or another should be avoided – much better to charge the battery overnight.

If you must use jump leads, use good quality heavy duty leads and follow this order exactly:

1. Discharged battery positive first, then running battery positive

2. Discharged battery negative, then running vehicle earth, ie engine lifting bracket.

3. The jump leads must not under any circumstances be allowed to short together or on either car body.

4. Before disconnecting reduce running engine revs and switch on discharged vehicles heated window or heater blower on full to reduce voltage peak

5. Remove leads in reverse order to 1 and 2.

6. Discharged battery should be mains charged as soon as possible – do not rely on the alternator.