Thankyou so far to members who have kindly replied to my previous messages. Unfortunately I am hardly any further forward with my dead'76 850Commando...no power - but then all of a sudden we got a rear light and horn/indicators working but no ignition or oil warning light - then fuses blow, BUT and this is where I am reliant upon other's (3 friends so far all baffled)help - we think the wires to the ignition switch may now be on wrong having had several pairs of hands on the ignition switch- would that cause a fuse to blow and for things to come on in the wrong switch position?
I have 4 positions, park (left turn off/remove the key), off,ignition on and then ignition with lights. What colour wires go where, we can't fathom the wiring diagram out now and that is so frustrating.Thankyou very much, I am no electrican and so want to get my bike on the road.
Russell
Russell Where in the count…
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Hello Russel Years ago Idi…
Hello Russel
Years ago Idisentangled the almost impossible to read wiring diagram of the MK3, and draw an electrical diagram(without starter cuircuit, with Boyer ignition,see attached). Maybe it can help to understand things better.
Remote debugging is difficult but I would try to check the 3 sub circuits (pilot, tail..... light,headlights and ign. horn, brake light....)one at time.Put the ign.sw. in pos. OFF, make sure the wireattached topin 1 is the one coming from the fuse (bat. neg. pole). Now use a peice of wire to bypass the switch, allways from pin 1 to one of the other pins.
In this way it should be possible to figure out if the wires to the sub circuits is placed the correct way. No matter how wrong you connect the wires to ign.sw. it should not be possible to blow the fuse.
It is most likely that problem is caused by either a broken wire or a bad connector, or a wire with broken insulation that shorts the battery, but how to find it ... 
Regards Leif
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Previously wrote: Russell…
Previously wrote:
Russell
Where in the country are you? I'd be wiling to help if you are reasonably local to Camberley, Surrey
David
David - thankyou so much for your kind offer....I am in Chesterfield Derbyshire ! so that's a little too far.
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Previously wrote: Hello Ru…
Previously wrote:
Hello Russel
Years ago Idisentangled the almost impossible to read wiring diagram of the MK3, and draw an electrical diagram(without starter cuircuit, with Boyer ignition,see attached). Maybe it can help to understand things better.
Remote debugging is difficult but I would try to check the 3 sub circuits (pilot, tail..... light,headlights and ign. horn, brake light....)one at time.Put the ign.sw. in pos. OFF, make sure the wireattached topin 1 is the one coming from the fuse (bat. neg. pole). Now use a peice of wire to bypass the switch, allways from pin 1 to one of the other pins.
In this way it should be possible to figure out if the wires to the sub circuits is placed the correct way. No matter how wrong you connect the wires to ign.sw. it should not be possible to blow the fuse.
It is most likely that problem is caused by either a broken wire or a bad connector, or a wire with broken insulation that shorts the battery, but how to find it ...
Regards Leif
Thankyou leif.
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Russell, Are you still in…
Russell,Are you still in the manure or have you been lucky enough to sort out the problem?I presume that you have a wiring diagram and colour codes to identify the various circuits. As previously stated by Leif it is difficult to sort out these things by text but taking each circuit in turn you should be able to identify the problem area with the aid of a test lamp, multi-meter, a fully charged 12v slave battery and a handful of fuses!I would gladly try to talk you through some tests but most often there is no substitute for actually touching the items. I have knowndifficultto see connectors to pull apart under the fuel tank along side of the main frame tube, similarly the harness connections inside of the headlight shell can be at fault, have you checked these out?If you are still having problems, could you transport the bike to Romiley, Stockport, and I could try to help you out?Hugh.
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Previously wrote: Previous…
Previously wrote:
Previously wrote:
Russell
Where in the country are you? I'd be wiling to help if you are reasonably local to Camberley, Surrey
David
David - thankyou so much for your kind offer....I am in Chesterfield Derbyshire ! so that's a little too far.
David - if you are desperate to help someone to fix their bike, I could do with some help. I'm at sledgehammer stage now - I really am! I just happen to live in Camberley...
Russell- my deepest apologies for invading your "thread"; take the battery out, tank, side panels and seat off - make the best access you can make. Disconnect every connector on the bike starting from the bottom (stator connections), and working methodically upwards. Here is the important thing - photograph everything prior todisconnection. Just try to remember that allseparatecircuits and ancillarydevices(lights etc) need an electrical supply and an earth; other components such as headlights and starter motors etc., normally require a relay to handle the highercurrentdemand.
Treat every "device" or circuit as an individual device and don't get confused with other cct's that share the same ground or supply or whatever on the diagram. I just did mine, this process is tortuous but very thorough - like a jigsaw without the box lid. Don't be scared and do use an ohmeter to buzz cct's through. Be patient, and god help you if you have to resurrect the starter motor drive gear train and cct... Good luck.
Oh and where you can, ALWAYS solder connections (leave a couple of inches of spare wire for if you ever need to cut it to disconnect - a "service loop").
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Russell
Where in the country are you? I'd be wiling to help if you are reasonably local to Camberley, Surrey
David