1975 Commando Rebuild

D

DaveinCanada

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Oct 27, 2024
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Hi All,

I've inherited a 1975 850 Commando motorcycle and going to attempt to rebuild it. I have ordered a new battery and installed it. However, none of the lights came on after turning the ignition key. I assumed at the very least, I would get the headlight or rear lights to come on. What am I missing? How do I diagnose if there is power going to the accessories etc? I know this is a newbie questions, but I'm a very green newbie and need some help to begin. Thanks.

Dave in Canada
 
Congrats on a nice inheritance. Electrical issues are my weak spot. That being said, check the most obvious place; the fuse in the battery main wire. Also, if the bike has sat for some time, turn the ignition key back and forth several times as the contacts have likely got some level of corrosion on them. Beyond that, happy hunting.
 
A good workshop manual is a good start. Also the parts catalogue for ordering. Keep in mind when fiddling with the electrics that these machines are +ground(earth) if it is a stock setup. And any history or records you can dig up may prove helpful for your project.
 
Look for NORTON COMMANDO RESTORATION (a book) on line. Buy a multimeter, if you don't already have one. Most parts can be ordered from Andover Norton and will land on your doorstep in 10 days or less. Don't be shy about asking questions on this forum, you will get a LOT of help and encouragement. Once you get your Norton repaired, you will have a powerful, fun bike that will turn heads. Go for it!
 
LPCityNorton said:
Congrats on a nice inheritance. Electrical issues are my weak spot. That being said, check the most obvious place; the fuse in the battery main wire. Also, if the bike has sat for some time, turn the ignition key back and forth several times as the contacts have likely got some level of corrosion on them. Beyond that, happy hunting.
Click to expand...
Thanks. It is a full bike that was stored for over 30 years in basement. Just to be sure, the wire with 35amp fuse goes to battery negative, right?
 
BERT said:
A good workshop manual is a good start. Also the parts catalogue for ordering. Keep in mind when fiddling with the electrics that these machines are +ground(earth) if it is a stock setup. And any history or records you can dig up may prove helpful for your project.
Click to expand...
I got a manual with the bike. I'm working on getting more materials if I can.
 
nortonmargie said:
Look for NORTON COMMANDO RESTORATION (a book) on line. Buy a multimeter, if you don't already have one. Most parts can be ordered from Andover Norton and will land on your doorstep in 10 days or less. Don't be shy about asking questions on this forum, you will get a LOT of help and encouragement. Once you get your Norton repaired, you will have a powerful, fun bike that will turn heads. Go for it!
Click to expand...
I will look for that book. I do need a lot of help getting this restored. I've never restored a motorcycle before. This is my first bike ever. Right now I just want to get power to the lights as a first step.
 
Check fuse for continuity with a test lamp or multimeter. If replacing, note that oem were 35A blow rating (a brit standard), not the 35A continous rating used on North American vehicles. So get something around 15A or 20A if buying North American fuses.
Does your new battery need activating/pre-charging? Multimeter can tell you what voltage it makes just sitting there...should be 12-12.5v at fully charged.

If all that looks good, next you need to consider if the ign switch is working by testing connections with test lamp of multimeter...they do go bad internally but can be restored or replaced. Of course a bike that has sat for long periods could of suffered mice chewing through wiring and or the Lucas bullet connectors corroding and/or breaking internally so those need checking.

Put some oil down the spark plug holes, just a few teaspoons will do, and let it sit a day or two befoee trying to turn engine over or start. Take the carbs off and do a complete clean out, checking jets are clear.
 
The MK3 should have a heavy starter ground cable connecting battery positive to the engine casing if you intend to use the starter motor.
1975 Commando Rebuild
DaveinCanada said:
So the wire with fuse goes to ground?
Click to expand...
No. You have a manual so look where the fuse is on the wiring diagram.
 
I'm not much of a hand holder, so...

The bulbs might be burned out.

Get a book before you start your garage on fire. ;)

You really need some hands-on help if your mechanical and electrical skills are not that great. YouTube might even be useful.
 
For a conductor ( the pathway along which the electricity flows ) to function it must be continuous from one end to the other , hence the term continuity . Conductors that you will be dealing with will be , for the most part , wire . You can check for continuity with a test lamp or buzzer . Touching the leads to the end points of the conductor in question will light the lamp or sound the buzzer if the conductor is continuous . If it not continuous ( broken , blockage by corrosion, switches off or dysfunctional , fuse blown etc.) then you will not light the lamp or sound the buzzer .
As nortonmargie suggested a multimeter is a good investment- most have a continuity test function with a buzzer . If you cannot afford one a battery , light bulb of the same voltage as the battery and two wire leads will suffice .
 

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