Electrical system

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Wiring diagrams:

For military Nortons, a number of  6V negative (-) earth systems have been used based on the existing equipment or the operational requirements of the time at which they were applied. It was a relative simple system and used by most of the contemporary British motorcycle manufacturers. Some used Miller equipment.
Lucas supplied both the ignition and lighting system components in the form of the Magdyno, a combination of a magneto to feed the spark plug and Dynamo to deliver power to the (many times troublesome) lighting system.
On all military Nortons, the lighting switch and Ammeter (if applied) were mounted into a small panel which in turn was screwed onto the top backside of the Lucas DU142 headlamp shell. On civilian motorcycles, owners had an option to mount the electrical equipment into a panel mounted on top of the petrol tank. These motorcycles were then provided with a completely closed headlamp shell type Lucas D142.

"Lucas invented darkness" or Lucas "Prince of darkness" are some of the many adjectives for the products of Lucas manufacture. Many of the problems were caused by bad maintenance or by the harsh environment into which the bikes were operated.

There have been 2 basic electrical equipment systems where the later version was used in four different electrical wiring schemes.

Electrical equipment variation one:
The first machines of 1936 did not have the luxury of the later introduced CVC (Compensated Voltage Control), but had to do with a switch to have the dynamo disconnected, at half charge or at full charge. A wire coil resistor mounted to the headlamp switch panel was used to "burn-off" the excess of power when the system worked at "half charge". This system is also described as the "three brush dynamo"  system.
The system worked using a switch with "OFF", "L" and "H" positions. When the battery was full, the rider could set the system to "OFF", in which case the dynamo was disconnected from the system. When the battery became discharged, the rider had 2 choices, half charge "C" for riding without the lights or lights on and full charge, switch position "H". The dynamo for this system was provided with an electro-magnetic cut-out which connected the dynamo to the charging circuit as soon as the dynamo voltage rises above that of the battery and disconnected the dynamo from the charging circuit when the dynamo voltage dropped below the battery voltage, to prevent the battery discharging itself through the dynamo.
It is relative certain that only the 1936 WD machines used this system as the CVC was introduced in 1937 which led to the "Norton 1937 specification" annotation which was the standard for all machines after that.

Electrical equipment variation two:
The CVC (Compensated Voltage Control) took the worry of proper charging from the rider and is basically a electro-mechanical regulator. It regulates both Voltage and Current by two coils working as electromagnets activating electrical contacts when either Voltage or Current exceeds a certain maximum value. The dynamo did not have the cut-out as mounted on the previous machines. T
he regulator (CVC) was factory mounted on the right hand upper rear chain stay above the tool box. In military use, these boxes sometimes changed position to the opposite left hand side upper rear chain stay. Ease of access to the wiring was probably the driver for this "field modification". 
Regulators working on the same principles were used throughout the motoring industry of that time until replaced by the electronic versions of today.

The wiring diagram changed over the years either to cater for the change from the   

           sused until 1941 was the basic civilian scheme having the 3 position headlamp switch (U 39). "OFF", "L" (pilot bulb and rear light) and "H" (main bulb and rear light) and an additional High/Low beam "Dip/Dipper/Dimmer" switch mounted on the left hand side of the handlebar. Civilian bikes had a brake light option. All military paperwork shows systems without the brake light so it is assumed that that they were never used on military bikes.

T position switch introduced between Oct 21st (latest known original MC) and somewhere in December.

On May 5th 1941, DME Circular B.141 mandated the removal of the Dipper switch from the existing motorcycles and the fitting of new headlamp masks (black-out).
Before that, the switches on new motorcycles were already replaced  in favour of a 4 position switch
(RS 39) with  "OFF", "T" (tail lamp), "L" (pilot bulb and rear light) and "H" (main bulb and rear light) positions. (Pictorial evidence showed that this ruling was not always followed. Most likely it was only done during major overhaul or rebuilding of the bikes). The newly introduced "T" position giving the possibility to have only the rear light working, an option apparently introduced for convoy duties.
With the introduction of the black-out mask, there was little use of the dipper switch arrangement with High/Low beam option.  The bulbs were now double filament, giving a spare filament in the same bulb.

Nearing the end of the war, an "improved" wiring scheme was introduced, to reduce the number of wires running from the front fork to the rest of the machine after it was recognised that many electrical faults developed through chafing, resulting from the continues movement of the front fork. This system was also introduced on other brand motorcycles like the BSA M20.
A late wartime Norton maintenance and instructional manual describes a modified electrical system. This system consisted of the deletion of the ammeter, and introduction of a push button in the headlamp panel to change from Pilot to Main bulb and a "new" switch (U39-L15) mounted at the right hand side under the saddle. With this configuration there was only one lead left from the frame to the headlamp.
The small panel on top of the headlamp shell was made without aperture for the ammeter, and a smaller hole to fix the push button in.
The switch had also 4 positions : "Test", "Off", "T" (tail only) and "H" (tail and headlamp on). The test position connected the D terminal of the dynamo directly to the tail light. The brilliance of the taillight was then supposed to be a measure for the operation of the charging system.  

Lamps were 24W main bulb (double filament), 3W pilot bulb and 3W tail lamp bulb. On the Big 4 the sidelamp and axle flood light were also 3W bulbs.
An "Altette" horn complemented the system where the early bikes used the HF935 and the later used the HF1235, operated through a horn push button on the right hand side of the handlebars.

iring diagrams for 16H and Big4 are basically identical apart from the additional sidecar/axle flood lights and wiring thereof.

It appears that the military machines did not follow the Lucas given colour codes for all periods. Up to October 1939 the dipper switch wire was a combination of red, blue and black wires in one sheath whereas the Lucas drawings all give 1 blue & white and 2 blue wires in one sheath.
The wire from the switch to "A" of the CVC regulator is coded red & yellow on early machines and purple & white on the later machines.
The wire from the switch to the tail light is coded red/black on the earlier machines but coded  red on later machines.

Colour codes for the simplified scheme are unknown but expected to be in line with the earlier where similar.


pre 1937

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1937 to 1941

1941 to 1944/45?

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1944/45 upwards


On  unrestored remains of a machine from Contract C5109 (1939/1940) the following was observed:
The wires were tin plated copper wires covered with rubber insulation. Identification was through coloured rubber sleeves near the terminals. The dipper switch wire was like a present day 3 lead wire with blue coloured individual insulated leads combined in one outer cover.
Note:   These early rubber covered wires used tinned copper leads because the sulphur in the vulcanised rubber leads to oxidation of the copper.

             Rubber itself deteriorates through the exposure to oxygen and UV radiation, becoming very hard and brittle
. For this reason not many original looms still exist.


Remains of original wires found on a  switch as applied in the late war electrical system (1944/45) appeared to be rubber like, similar as described above.
This indicates that rubber encapsulation was used during the entire war.

Picture from article of Steve Madden, courtesy Henk Joore's website.

At least 2 different diameter wires have been found, approximately 4,6 mm and 5,7 mm as measured on the insulation.

Wiring remains on a late-war (re?)built machine showed to have cloth covered leads. It was not possible to assure this was factory applied. Whether the use of the cloth encapsulated wire was widespread is difficult to say. Cloth encapsulated wiring was used on motorcars and motorcycles in the 20ties and 30ties.

Wiring harness and wire fixing
The main wire loom was protected by a rubber sleeve from the headlamp shell mounted switch panel through a loop clamp on the right hand side of the front fork, under the upper frame tube until the saddle tube frame casting. From there on the individual leads went to the Dynamo, CVC, and tail light. The life horn wire ran parallel to the wire loom/rubber sleeve from instrument panel directly to the horn. The horn earth wire ran directly from the horn to the handlebar push button. The battery earth wire was fixed to the top battery carrier stud.
Attached pdf "Wiring harness cable clamps" shows the clamps and positions as best as I have  been able to reconstruct. I do not claim to have it absolutely correct but it is better than ever seen before,
which is nothing!

Batteries and CVC regulators
It is not exactly known which battery type was used on the 1936 built machines.
From 1937 onwards, the military machines were provided with a fairly lumpy Ni-Fe (Nickel-Iron) alkaline battery.
These Ni-Fe batteries were purchased under the Lucas name "C105 Ni-Fe battery" but in actual fact produced by the "Batteries Ltd. Redditch" company. The inside of the lid states "expressedly made for Joseph Lucas LTD Birmingham England". A more elaborate description of the Nife batteries can be found here
First mention of the Ni-Fe type was in the 1937 Norton assy books and the last use of it was registered in October 1939.
The Ni-Fe batteries were eventually replaced by the more "normal" Lead Acid type batteries, primarily the Lucas PUW-5E and equivalents later in the war.

Because of the different charging requirements there were also two types of MCR1 CVC's. Each clearly marked with either "Ni-Fe" or "Lead Acid" above the FADE markings. The "Lead Acid" marking was finally deleted around 1941 when the Ni-Fe's were all replaced by Lead Acid batteries and the distinction was not necessary anymore. Lead Acid batteries could work with Ni-Fe CVC's but it was only allowed for a short period and not recommended.

Many (but not all) Lucas parts are provided with the manufacturing date stamped into them. If you really want to restore a bike to "factory" fresh condition, searching for correctly dated Lucas equipment should make your life exciting.

Actual equipment:

The Electrical equipment picture page gives some indication on what the different parts basically look like.