Hi Alex
I think all the components would be hard wired without Lucas type bullet connectors, which did not appear on the scene till the late 1940s. The wires certainly be rubber insulated with a fabric covering, a rubber sleeving would be used to carry all the wires that come together near the cutout mounted under the front of the tank up to the headlight.
The F/G models were fitted with the Bth Mag/dyno. The dynamo probably produced all of about 15 watts on a good day. This would hardly balance the headlight load. The dynamo is a permanent magnet type (similar to the pancake type) and as such does not need to use a CVC (constant voltage control) unit or regulator as used on the post war machines. It will of course need to use a cut out or reverse current relay, which senses when the dynamo output is high enough to start feeding current into the 6v. system. At that point it will close its contacts and stay closed until the output of the dynamo falls below 6v., whereupon current would flow backwards to the dynamo unless the contacts open. With the contacts open the dynamo is disconnected from the system. Because there is no control of the voltage as such, unlike the post war set up which regulated or reduces the field current of the dynamo once the output voltage reaches 6.8v., which is the on charge voltage of a 6v. battery. Thus the constant voltage control, the earlier method of controlling the current and voltage was means of the 3rd brush system, whereby to prevent overcharging of the battery a series resistor was incorporated in the headlight switch and was in use unless the headlight was in use. The Bth used a similar system incorporating a series resistor.
In the sightly earlier BTH headlight, i.e. fitted to machines in around 1930, with a large bakelite rotary switch at the rear of the headlight. It was a 4 position switch with the following positions, Full, Dim. Charge & Off. I cannot remember what the later P & H headlamps with the cast aluminium switch knob, which would have been fitted to the 1931 models, had on the switch but I am pretty sure it too was a 4 position switch. No dipswitch would have been fitted originally as a single contact headlight bulb of 12w. would have been fitted, together with a 6w. park bulb. The four position was Off, presumably the charging system was off but I am not sure how this was achieved, unlike the Lucas system which did not generate at if the field circuit of the third brush was open, Dim presumably was the park light, Full switched on the headlight bulb, and Charge being used to charge the battery during daylight running.
When double filament bulbs (which appear to have come into regular use on English cars around the late 1920's) became available, it was some years before they became mandatory. It became a requirement have dipping headlights on all vehicles in New Zealand in July 1939, this required the replacement of the headlight bulb holder, for one with 2 contacts. It was also necessary to fit a dip switch, or reconfigure the headlight switch so that the system was charging in the charging position, the off position became the park light, and the high/low headlight was operated in the Full/Dim position, this avoided the use of a dip switch. My H3 of 1930 has been rewired in this manner, but unfortunately it has a Lucas headlight not a Bth with the rear switch. No brake light switch was originally fitted. I am not sure what the original hooter button was like but it may well have been an insulated metal strip which was pressed against the handlebar.
Hope my ravings may be of some help
Best of Luck with the restoration
Steve L
