Dommie 99 rectifier polarity and other issues

Dommies had a number of different wirings. So year of make could give a clue. But many of them have had changes done. All of them left factory with positive earth. Not all today.  Lot of them have no fuse connected to the battery. Fitting a fuse between battery and earth, as Norton did on some late machines is a good way to prevent a reversed battery to cause the famous Lucas smoke or killing rectifier and Zener.

I'm not certain if there ever was any negative earth zener diodes, all I've seen has been for positive earth systems. Anyhow you have to test both zener and rectifier. It would not surprise me if battery terminals isn't accessible when fitted. Have a couple of vehicles like that.

If you connect the battery the wrong way round the ammeter will move the wrong way when you turn the lights on. If you have a modern rectifier/ regulator you should diconnect that beforehand. 

HELLO now the  model 99 from september 1957 on electrics were on 6 volt and alternator was a RM15 3 wire and a ignition and lighting switch was the PRS8 so the wiring will be from this and had distributor ignition the D2 So the magneto as been fitted by a previous owners  and all Nortons from bracebridge street  are positive earth And the white with black tracer  is for coil ignition wire         yours  anna j

.. my 1952 ES2 which is definitely from Bracebridge Street is negative earth and left the factory in that state (at least according to Edgar Franks).

irrespective of what it was when it came out of the factory, It has now changed so start from scratch.

If you have a small 4 terminal rectifier and the positive goes to the chassis of the bike, you have positive earth.

You can yet -ve or +ve Zeners but is most likely a positive earth zener.

If you have connected the battery up the wrong way round, you have possibly blown the rectifier, zener or maybe just (if you are lucky) a fuse.

You will not have damaged the alternator or ammeter.

So, start out with the zener and rectifier removed from the circuit and find out why volts from the battery are not getting to the lights. Switch / fuse / burnt wiring / incorrect wiring. Once you have done that, you should be clear which is positive and which is negative. 

Connect the zener back into circuit, lights etc. should still work.

Connect the rectifier back in circuit, lights should still work.

Start the bike and see if it charges. If not you have probably blown rectifier up. If it charges but the volts go above say 14V then the zener is toast.

Regards

Tony

The book written by Edgar Franks (who as you will know was a senior designer at Bracebridge Street) which covers my model has a wiring diagram showing negative earth. I would expect that the Model 7 of the same vintage as my ES2 would have been similar.

Workshop manual for 1954 16H, Big 4 18 and ES2 shows positive earth.

Workshop manual for exactly the same list of bikes but without a date shows negative earth. 

Does this help  or add to the confusion?

Can provide pages from the manuals if you want them.

Tony

We could argues this subject for years-some facts, as far as I can ascertain Nortons were Negative earth up to 1952. 1953 all Nortons from the factory Positive earth. IF you know otherwise prove it, i.e.  show me the document?

Mikael R- Nortons never fitted a fuse in the Earth line either. (Triumphs did). It would also appear that Fuses only came in from the factory with the Commando (and perhaps the last of the Atlas, Mercury). But of course fitting a fuse to any 12V bike is almost obligatory, 12V has a nasty habit of getting out of the battery into the wiring and causing smoke and grief. 

Zener diodes-80% of these were positive earth. The modern square 4 terminal rectifier, if bought from a reputable supplier should be virtually bomb proof, the alternator in this discussion is bomb proof and the connections to it are reversible. In this saga there are battery wires of the wrong colour-why do you do it? It adds to every ones confusion, non working, smoke, expense. Your choice.

Peter Brown-if you need any more advice, wiring, please get in touch  aoservices.co.uk

.. I always fit one in the battery earth cable as it's so easy to short out the live terminal with an errant screwdriver etc. Yes I have done this......

Of course this works for both negative and positive earth.

The Edgar Franks book I referred to was first published in 1948: my edition is 1949.

Shorting the battery-easy done. There is a rule in the car world which remains true for bikes as well. You have to think about this-Disconnecting the battery-Earth first. Reconnecting-Earth last. 

Saves having a 'welding hole' in your screw driver. But the story above by Mikael R inferred that Norton fitted a fuse in the Earth line-they did not.

My mention of a fuse from battery to earth, came from the Norton twins Haynes manual for post 1966 models. Foolish of me to use only one source.

Very foolish to use Haynes-known for upside down pictures of the wrong part. But if all else fails they can be a starting point. OK Mikael

Checking the Norton Spares parts list, which is a somewhat more reliable source. The only ones before the Commando to have a fuse holder seems to be the P11 and P11A.