I have a 1973 850 Commando, which had been starting and running well until I replaced the battery.
I had some trouble making the connections to the new battery; it appears that the bike has been wired with a negative earth. I therefore tested the obvious negative connections with a circuit tester and made the connections appropriately.
They were as follows:
Large earth cable from an earth point near the right hand side Z Plate
Three red wires attached together with an earth label on them
Black Wire from the Voltage Regulator
The Live connections were as follows:
A red wire with in line fuse
A red wire from the voltage regulator
All the electrics work as they should; lights indicators, horn etc, but I have no spark when kicking it over.
The bike is fitted with Boyer Bransden Electronic Ignition and I think I may have damaged the control unit by connecting the bike initially as a positive earth?
Having removed the tank, the original loom is a mess with poorly crimped connects here and there. I am considering replacing the loom completely!
However as poor as the wiring appears the bike started and ran well before I changed the battery! Could it be that I may have damaged the electronic ignition module?
Thank you in advance.
Mark Newman
Evesham
Did you connect the battery…
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YES BUT.......
There is every chance that the Boyer ignition unit has been 'killed' by reverse polarity. I can test it but it is better to send it to Boyer Bransden. If it is only the amplifier box, that will have died, they are less than £100
Checking out wiring in this situation with a 'circuit tester' is virtually a waste of time. The bike CAN be negative earth. What you have to consider is....any electronic ignition and any battery charging has to be altered also LED lamps have to be corrected (LED flashers). Ignition coils will not be harmed and they will still work (reverse polarity) but the spark will not be as good. I personally would NOT do this without a complete rewire other wise you have a RED wire Earth and even on the battery in which case you end up in a Mucking Fuddle as per. Carry On.
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Update
Thank you for your replies so far, I emailed Boyer Bransden and they immediately replied saying that any reverse polarity damage would be either to the Voltage Regulator or the ignition.
I can send the old unit back for testing, but it is clearly relatively old, I can get a brand new one for £115!
Any advice on replacing the loom, Genuine Lucas ones are available relatively cheaply.
Thanks again
Mark
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More correctly 'Lucas'…
More correctly 'Lucas' branded. The Lucas name is now owned by Wassel.
New looms are available either cloth bound or PVC tape bound. I'm not keen on the cloth bound variety, i find them far too stiff to mould around the frame and the cloth covering holds all the oil and shite that the engine expresses. That said, i prefer to make my looms as you can customise it to your exact requirements. For example, you can get rid of all the under tank sleeve connectors and put them in the headlamp shell. Neatens things up and reduces the amount of bullet sleeves used (less connectors = improved reliability) Al Osbourn sells a kit to rewire bikes. That is if you can read and understand the wiring diagram in the manual!
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You don't have to.....
You don't have to understand the wiring diagram, they are all the SAME. If you follow the British Vehicle wiring standard from the 1960s and follow the colour code it is easy. The colour code comes with my wiring kit-see the web site A O Services.co.uk
If you just want the bike to start/run then of course you have to replace the Boyer amplifier and connect it with regard to CORRECT polarity with respect to the battery. initially you do NOT have to worry about any voltage regulator. Disconnect for the moment. decide if it is Positive or Negative Earth, connect the battery thus and the BB ignition then start the engine. The lights and horn will not care re polarity, but any LED lamps will The bike WAS positive earth it should have a RED wire throughout the loom.
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If it were me.
If it were me I would not buy a new harness as a lot of the wires will be redundant as you have electronic ignition etc.
Make your own it is not difficult and there are good wiring diagrams on the net for modified neater setups. I prefer original bullet and spade connectors for Norton's and a good set of crimping tools and a soldering iron and your away.
It is also very rewarding and neater.
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Sounds terribly familiar
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BB?
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POS -NEG??
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Did you connect the battery the 'right way' round. i.e the same as it was with the old battery. Or did you initially connect it the other way round?
Positive or negative earth does not matter as long as everything is the same way round.
Lights and horn do not care.
When you say 'regulator' is that the simple rectifier and Zener or something modern?
I do not know if the electronic ignition has reverse polarity protection (anyone know?).
If the only thing you have done is changed the battery and you did connect it the wrong way round initially, and now you have no spark. I think you know what the answer is, and it is expensive!