Engine Bay Wiring

Figure 1


Notes on Removing the loom

During the rebuild of a Morgan it is wise to keep a notebook and record every detail of the components and their relationship to one another. The sketches I made in my notebook when stripping out the wiring made the job of reassembly so much easier. Removing the electrics is usually one of the first and last jobs in a rebuild, so it is often a long time between stripping and reinstating it. Unlike the re-assembly of mechanical parts which appear quite logical, the tangle of coloured spaghetti can appear dauntingly abstract, but if labelled and recorded properly it is quite straightforward. Don't worry if you feel your notebook drawings are untidy. The important thing is that the diagrams mean something to you. In "Haynes Automobile electrical & electronic systems manual" (ISBN 1 85010 588 X) there is a copy of C.F. Kettering's patent sketch of his battery ignition system. It looks like an artistically challenged 5 year old drew it, yet it clearly illustrates the principle of Ketterings coil & points ignition invention. Of course the man was a genius (one of the most prolific inventors of the 20th Century) who I have no doubt produced immaculate technical drawings of his inventions such as the electric cash register.

Always disconnect the battery before dealing with the wiring and refer to the circuit diagram in the "Morgan Owners Handbook" for your particular car. If you do not possess one you will find circuit diagrams dating back to 1936 in " Morgan Four owners workshop manual - Autobook 796 " by R Clarke. On close inspection of these diagrams you will notice letters denoting the colour of the wire to which they are adjacent. The Lucas colour coding system of automobile wiring was used on Morgans manufactured in the 1970's. 7 main colours and various tracer colours were employed. In the circuit diagrams the first letter represents the main body of the wire followed by the trace colour. Always try and use the correct gauge, length and colour wire when replacing damaged parts of the loom. The Holden Vintage & Classic company will probably be able to supply you with most electrical wire & components for an old Morgan. The circuit diagram (W54955381) in the 'Morgan Owners Handbook' 1972 may confuse owners of vehicles manufactured around this time, because of differences in the alternator wiring. The wiring shown is that of a battery sensing alternator which requires three extra components under the bonnet. Alternator terminals F+ & F- are connected to an external alternator relay and control unit. The AL terminal is connected to a Lucas 3AW warning light unit. Nowadays most vehicles have machine sensing alternators (often referred to as self-exciting) which have an electronic regulator built in and do not have these 3 external units.All Morgans built since 1972 possess a self exciting alternator. They usually only require two wires as shown in Figure 2 below.

Before disconnecting the wiring in the engine bay is it is necessary to withdraw the wiring loom from under the wheel arches. Note where the wires are attached to front bumper tubes, lamps, horn and inner wings etc. then carefully disconnect the loom from them. Now withdraw the loom through the inner wings into the engine bay.

Disconnect the loom from the following:

Fuse box
Ignition coil
Ballast resistor
Starter solenoid
Brake stop lamp switch
Dual brake switch
Engine temperature sensor
Screenwash bottle and motor
Windscreen wiper motor
Engine (earth wires secured to timing cover bolt)

When the wiring loom has been released from its retaining clips and disconnected from all of the components above, it can be withdrawn through the bulkhead. It will now be necessary to remove the dashboard wiring .

Figure 2

Morgan under bonnet wiring

Notes on Replacing the loom

A good restoration should require the car being assembled as near as possible to the way it left the factory and little details can matter. Sometimes it may be necessary to replace components in the interest of safety, particularly where the electrics associated with brake components are concerned.If you click on the brake switch link above some of these problems are high lighted. One particular example of deviating from the original wiring in my own car was putting extra clips on the nearside inner wing for the brown and white wire connected to the B+ terminal of the alternator. I once adjusted the fan belt on a winters evening in poor light and ended up with a burned out ammeter & B+ wire. The excessive length of that wire allowed it to touch the exhaust manifold which is extremely close to the alternator. Having driven a short distance smoke appeared under the dashboard. Fortunately I managed to stop, switch off the engine and pull the wire away from the manifold before matters worsened. The wire had not totally burned through. If it had, the alternator would have probably been destroyed. As luck would have it repairing the ammeter was simple. It was of the fixed coil type which are often used where large currents are measured. Inside the instrument the coil consisted of one loop of heavy gauge wire. I obtained a some wire of the same gauge , copied the length and shape of the old coil remains and soldered it back in position and it has worked well for the past 40 years!

With increasing speed and disconnected from a load, the output from an alternator can reach in excess of 100 volts. Never run an engine with the alternator disconnected and always make sure the retaining clip on the wiring connecter is in good condition & secure. Nowadays any insecure wiring will be picked up during an MOT.

Main ignition circuit components

Figure 3