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 cuased by bad maintenance or by the harsh environment into which the bikes were operated.

There have been 4 variations of the basic system used on the military Nortons from 1936 onwards.

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 disconected, 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".
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 dischargeing itself through the dynamo.
It is relative certain that only the 1936 WD machines used this system.

In 1937, this system was replaced by the CVC system which was used until the last military bikes were made. The CVC 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. The 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 for ease of access. 
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 used 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 Ligh/Low beam "Dip/Dipper/Dimmer"switch mounted on the lefthand 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.

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, givig 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 HF934 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.


pre 1937

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1937 to 1941

1941 to 1944/45?

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1944/45 upwards


On a very original, unrestored machine from Contract C5109 (1939/1940) te following was observed:
The wires were 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. The wire loom was protected by a rubber sleeve from the headlamp shell mounted switch panel through a loop clamp on the front fork until the saddle frame casting. From there on the individual leads went to the Dynamo, CVC, horn and tail light. The rubber sleeve was fixed to the frame tank tube using metal clamps. The tail light wire was clamped to the right hand side of the rear mudguard by means of 4 small clips. 
Another surprise, the ammeter was a CZ27, but it showed to have a domed lens. Until now only flat lenses were observed! 

Wiring remains found on later built machines showed cotton covered leads for all wiring. This was most likely the result from the loss to the Japanese of rubber producing countries like Malaysia in 1942. This led also to the introduction of steel footrests and canvas covered handlebar grips.

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.