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1959 Dominator 99 rewire



I wonder if anyone can help with my rewire problems please.

The bike was a just-about runner and I'm slowly working my way through a long list of issues the next of which is the electrics. 

The bike is a magneto ignition and I got it running without the battery or any electrics. 

I've got the heavy twin manual and am referring to the wiring diagram "for 650 Std and de Luxe, 99 std, de Luxe and SS, 88 Std and de Luxe". 

My specific problems are;

1: I am confused about the coil and contact breaker. I do have an elderly white cable which goes nowhere but no coil (this could easily have been lost obviously). On the diagram this goes to the contact breaker though. Isn't this the distributor for a coil and points ignition?

If that's the case then do I just ignore the coil from the diagram as mine is magneto?

2: My alternator has 3 wires; red, black and green/yellow. Red and green/yellow connect to the rectifier and black goes to the PRS8 switch (although this is connected via a green/yellow cable on the main loom). The wiring diagram shows the green/yellow going straight to the switch. 

Should I just connect red and black to the rectifier? 

3: In an effort to spend myself out of the situation I bought a new Lucas 6v rectifier (49072). This has got 4 connectors (v 3 on the original and diagram) which a coloured (from stud to nut) red, yellow, blue, yellow.

How should I wire this???

Thanks in advance for any assistance.





Its clear that the bike was orriginaly a coil ignition model with the PSR8 switch.It can be wired up as original and the white coil wire taped up.A good idea to run with the sidelights on to use the current up and avoid overcharging.The system can be switched to 12v and a better voltage control system fitted and the wiring simplified. I expect Al OZ will be along soon to clarify.


Disclaimer: This is what I believe. I have been wrong once, so it could have happened again.

1. Ignore the white one. Just have it insulated.

2. Alternator. The two wires (red & green/yellow) goes to rectifier. The black one to the PRS8 switch will be connected back to one of the other wires when lights are turned on. Idea is that enough power for battery and coil ignition will be supplied. When lights are turned on, extra power will be supplied to the rectifier. A primitive  but usually working solution for not overcharging.

3. There are actually 4 connections both on your original rectifier and the diagram. Two from alternator (probably the yellow), one negative output (probably blue) and the 4th (also the stud) is positive ground (probably red). Only relying on the stud for ground is not reliable. To ensure good ground, wires needed at least from rectifier to battery and headlamp.

As Robert said, a rectifier/regulator is a much better solution for a happy battery. Either 6 or 12V. While waiting for definite and correct answers have a look at


Thanks very much for the replies, that's very helpful.

If it was originally coil and points then would it have had a magneto as well? It sounds like much more work to convert the ignition system rather than fix the existing?

If it's been converted to magneto ignition are there any reasons to change back?


I too have a 1959 99 and it originally had coil & distributor, but it gave me trouble so I swapped it out for my old K2F Magneto from a 1955 Dommie.  I think I swapped the PRS8 switch for an 88SA one but I can't remember how I wired it - it was about 55 years ago!  If you only have a magneto it makes sense to stick with it.  They tend to b e more reliable.  It will be expensive if you have to buy a distributor and coil.

Do you have a PRS8 switch?  In spite of what people say about it, if it's working it does the job of selecting the alternator coils to suit the lighting load.  All coils are switched in when you use the headlamp.  You don't want all of them feeding the battery without the headlight on as it will cook it!  For this reason an LED substitute for the headlamp bulb isn't a good idea, unless you change the charging system - ask Al Oz!   Upgrade to a Halogen bulb by all means - I'm sticking with 6 Volts.  The tip about running with daytime lights on is a good one.

There is a Norton Manual specifically for the 1959 year - Publication P100 - and it covers the 88, 99 ES2 & Model 50.  I have two of them - one printed in 1958 and was originally the AA's copy, date-stamped December 1958 - and the other is a 1959 print.  The wiring diagrams are the same as you listed as they use the PRS8 Switch.  The white wire went from Terminal 14 to the SW side of the coil.  You don't need this nor a Black/white connection from the coil to the contact breaker (Distributor) unless you are going back to distributor/coil ignition - like I am!  I kept my distributor and have refurbished it.  There are improvements you can do for the condenser - having a more robust external one, but that's another story!


Thanks again for the advice.

The plan is to switch to 12v, keep the magneto and the PRS8 and everything should be ok!



Most of what you say Lionel is correct. Except that you do not make the point very prominent  that the PRS8 when it is used for alternator coil switching it is ONLY for the 6V system. If you go to 12V then as Lucas Zener diodes are no longer available then you have to use a regulator/rectifier.

The alternator colour wires as quoted above are non standard but if they are connected wrong then the worse that can happen is low or no output for charging the battery. The PRS8 should work well enough on 12V, but I recommend full checking it out if you want to be sure of a good result.

Lionel you can do better that just fitting an external condenser you can fit full twin coil electronic, but of course you realy need 12V.

A lot of this is on my web site  no need to bore you further on here. Or get directly in touch.

Yes Al, I was assuming we were talking about 6V with a PRS8, not 12V where you just use the full output of an RM15.

I'm still sticking with 6V as riding in the dark isn't likely to happen much! 

I am considering an "electronic ignition" like I used in the late 1970s on my Bedford CA Dormobile and my Mark 10 Jaguar.  They worked OK (until the Bedford one filled with water!) and they claim to reduce points recession.  I wonder if anyone has used something like it with the Lucas 18D2?

They are here -

I'll post it as a separate question.


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