Firing (?) Up The Electrics

Well over a year ago, before our departure for UK, the cab wiring had been brought up to the point where starter, turn indicator, brake and parking lights would work but the interior lamps had been left as loops of wire hanging out of the bodywork. Their fuses had been pulled so that short circuits were avoided. Fuses are there for the good reason that if serious shorts occur, the fuse blows and cuts off power to that circuit before the bus catches on fire. You hope.
Once the ceilings had been painted, interior lamps could be fitted, along with buzzer pushes. As I came to fit the second buzzer push, downstairs on the left of the arched entry to the lower saloon, I noticed a gentle spark as the wire stripper bit into the second of the two wires. Odd, I thought: the fuse for that circuit isn't even installed. So I went to the cab, inserted a few of the seven fuses mounted on the bulkhead above and behind the driver's seat, to see what was what.
When I turned the driver's cab light on, the horn blew! Oh hell......
I had ghastly visions of wiring, fitted anything up to two years ago, having been penetrated by drilling and screwing to fit some body part, and so shorted to the body. Or, had I badly misinterpreted the peculiar separation of the four battery connections, which allow for 12 volt lighting (batteries in parallel) and 24 volt starting (batteries in series)? Don't panic, I thought, breathe deeply, go about this in a methodical way.....
Bit by bit, I checked circuits with a multimeter, and found that there was a dead short of the negative terminals of both batteries to the body. This should not be: the system uses two wires, a negative and a positive, for everything. So nothing, negative or positive, should ever contact the frame of the vehicle. (Unlike all motor cars of the last 60 years or more, which use the body as the return, so that only one wire is needed for each electrical item).
Proceeding along all the negative connections I eventually found the offender: the blinkers. These are off the shelf, car part shop specials, designed for using the body as the return half of the circuit, and so had had to be insulated from the body with fibre or plastic washers and sleeves. In the rush to get the bus mobile again at Loftus and get it back here, I had refitted the blinker near the driver's door with a discoloured steel washer, which looked like a fibre washer, and there was my dead short to ground (or body).

THE BLINKER BEHIND THE DRIVERS CAB DOOR. THE TWO PHILLIPS SCREWS HOLD THE FITTING TO THE BODY, AND ARE NOW CORRECTLY SECURED WITH RED FIBRE WASHERS. Don't tell anybody that there are Phillips screws here: historical accuracy demands that they be slotted head screws. Phillips had not been invented in 1937. When the orange lens is fitted they are out of sight.
Yet with that fixed, there was still a short circuit from the buzzer push wiring, to ground. Was there a bit of wire crunched between two body parts, and making contact with the frame? I desperately hoped not. There would be a lot of dismantling to get at that. So far I had only fitted one push switch, the one at the head of the stairs. I pulled it out, and tested again: short gone. The hole for the push switch was just that little bit tight, and with the "new" switch of appropriate appearance wired and fitted, there must have been just a vestige of contact with the surrounding metal. Phew.

THE CONDUCTOR'S BUZZER PUSH AT THE HEAD OF THE STAIRS. IF YOU THINK THE INTERIOR FITTING-OUT IS A BIT ROUGH HERE, IT IS: THESE BUSES WERE PUSHED OUT AT THE RATE OF TWO A WEEK TO DO A JOB. CARRY PEOPLE.
How could this have blown the horn?
Once I had sorted out the non-working interior lights: another story, but suffice it to say that fuses that after 50 years looked all right, weren't. Some had fuse wire that was corroded through where you couldn't see it. And one light switch made the right cliccking noise but no electrical contact. So, with new fuse wire all round, and one switch removed, cleaned and refitted, the interior lights worked, the cab light worked and didn't blow the horn, and the buzzer worked.


THESE TWO SHOTS OF THE LOWER DECK WERE TAKEN WITHIN SECONDS OF EACHOTHER, WITH THE INTERIOR LIGHTS ON, AND WITH THE SAME CAMERA SETTINGS. THEY CAME OUT QUITE DIFFERENTLY. The level of illumination is in keeping with the period: there are six lamps downstairs, each of 12 watts, making 72 watts in total. Not even the power of a 75-watt domestic bulb for the entire space!
The buzzer I now found was buzzing so well it sounded more like a horn: it had been the noise when the cab light was turned on, not the horn. The buzzer is adjustable, and on the bench I had adjusted it to its maximum, but fitted to the cab wall with all that metal to resonate against, it nearly made me jump out of my seat. the horn doesn't sound much different. Now it just hums politely.

THE BUZZER WITH ITS COVER OFF. The screw and nut in the centre of the circular diaphragm is the adjuster. In for louder, out for quieter.
I can see why drivers complained about the buzzer, and why post-war it was changed to a bell, which is more musical, and can be heard by driver, and passengers, and conductor, without having to be loud.
The scale of the buzzer is impressive: it is housed in a solid cast aluminium box, the electromagnet which operates it is the size of one of those tiny marmalade jars one gets in sets from Scotland, and it will last forever. Your mobile phone can produce hundreds of different ring tones, show pictures, send texts, etc etc and is about the same size. Technology....