Author Topic: Wiring diagram (Read 2501 times)

Alan · « **on:** 14 Apr 2020 at 04:21 »

For interest, a wiring diagram found in Motor Cyling Electrical Manual by Bernal Osbourne published 1953.
A bit confusing as I thought the T35 had been replaced by this date.

eddie · « **Reply #1 on:** 14 Apr 2020 at 06:58 »

No, the T35 went right through to 1953! What is confusing is the way Douglas changed the format of their labelling! The models started in 1947 (with the T35), the next model was the T35 Mk3 - as there was a subsequent model, the original T35's then got referred to, by the public, as Mk1's. At this point, the engine/frame numbers were getting rather long (as in T35/S/****/3), so from the Mk4 onwards, Douglas dropped the T35 prefix. At the time of the Mk3 production, the factory was experimenting with other models that never made it into production due to financial reasons. Because there were no other models planned for the range, the need to include the model in the frame or engine number disappeared. The end result is we have Mk3's, 4's and 5's spawned from the original T35 (which later got referred to as the 'Mk1' to differentiate it from the later versions, but they are all T35's).

Hope that makes sense,
Regards,
Eddie.

EW-Ron · « **Reply #2 on:** 15 Apr 2020 at 06:18 »

Is there a colour code for those numbered wires ?
Or does basic black cover them all...

It doesn't actually look any different to yer average magdyno system,
its just the layout and numbering makes it look neater ?
And they have adopted +ve earth already.

How does 20 earth out a magdyno ??

eddie · « **Reply #3 on:** 15 Apr 2020 at 09:00 »

Originally, all wires were black with numbered or coloured sleeves on each end.
The polarity changed during the production of the Mk series - I believe between the Mk3 and 4. The polarity doesn't make any difference to the actual wiring - it just requires the dynamo to be polarised to suit.
Wire 20 is the ignition cutout lead that goes from the points cover to the cutout button on the handlebars - pressing the button earths out the points, and kills the spark.

Regards,
Eddie.

P.S. As far as I am aware, there was no benefit from changing the polarity on motorcycles, but the car industry changed to positive earth in the 50's in the belief that it would reduce body corrosion. Since the adoption of alternators, the car industry has almost totally gone back to negative earth - so I guess that dispels that myth!!

EW-Ron · « **Reply #4 on:** 15 Apr 2020 at 21:41 »

Wasn't there some discussion that the early selenium rectifiers were built as +ve earth,
so motorcycles went +ve earth in anticipation.
Which doesn't explain how USA etc cars stayed -ve earth....

My magdyno (not Douglas) doesn't have any provision for earthing it out via a stop button,
so how does that work ?
(most single cylinders use the decompression lever as a stop engine function)

Alan · « **Reply #5 on:** 16 Apr 2020 at 03:56 »

Apologies..should have attached this and as Eddie said..mostly black.
Also attached Mr Osborne’s thoughts on why pos or neg earth..sounds all a bit theoretical!