75 Commando / No Headlight or taillight

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mrmach5

mrmach5

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Riding to a bike event with a friend last week and discovered no Headlight, hi beam or low, no pilot light and no tail light. Tested for power at the headlight and none. the manual mentions a fuse? but no location. Any way could someone point me in the right direction, and if no fuse , where to start.
Thanks!
 
mrmach5 said:
Tested for power at the headlight and none. the manual mentions a fuse? but no location.
Click to expand...

The standard electrical system has only one fuse and that should be close to the battery on the brown/blue negative wire (assuming normal positive earth/ground?).

The headlamp is a separate circuit to the other lights (tail, pilot, instruments) so you have a possible fault on two circuits or the problem could be inside the ignition switch.
 
Main fuse is not blown. Turn signals work, brake light works , just head and tail lights not functioning.
 
For both circuits to have failed simultaneously (as far as we know) suggests a possible main switch fault.

The headlamp supply from the switch is blue/yellow [UY] normally connected to main switch terminal 4.
From the headlamp selector (Head-Pilot) switch in the right-hand cluster it is then blue to the dip switch (Hi-Lo) in the left-hand cluster.
Tail, pilot and instruments are fed by brown/green [NG] connected to main switch terminal 3.
To bypass the switch, temporarily connect UY and NG to brown/blue [NU].
As the brake light is still working it seems less likely to be an earth/ground fault but perhaps it can't be ruled out completely.
 
mach5,
Start inside the headlamp shell and work backward and under the tank at the connection terminals. Follow the wiring diagram with a test lead/bulb or voltmeter. You may have a bad connection at the rubber bullet terminals. they tend to disintegrate or split with age. See if power is getting to the switch gear at the bars, Key switch etc. Taking the tank off will greatly help your fault finding.
Cheers,
Thomas
 
CanukNortonNut said:
Start inside the headlamp shell and work backward and under the tank at the connection terminals. Follow the wiring diagram with a test lead/bulb or voltmeter.You may have a bad connection at the rubber bullet terminals. they tend to disintegrate or split with age.
Click to expand...

Unlike earlier models, the standard 850 Mk3 main harness connections under the tank are plastic multi-pin plugs which also corrode. The switch cluster wires feed into the headlamp shell (again connected by multi-pin plugs).
 
75 Commando / No Headlight or taillight
FWIW
In addition to the main fuse near the battery I have at least one other fuse and possibly two in the headlight shell. I know for sure one is on the white wire. These appear to be factory and had Lucas glass fuses in them.
Pete.


Edit
Actually three fuses. They have been there as long as I have had the bike (27+ years)
 
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LOL L.A.B. you got me again.:oops: I need to shut my piehole when it comes to MrkIII's until I own one.:rolleyes:
but still trouble shoot the same way as I said.
Cheers,
Thomas
 
Deets55 said:
In addition to the main fuse near the battery I have at least one other fuse and possibly two in the headlight shell. I know for sure one is on the white wire. These appear to be factory and had Lucas glass fuses in them.
Click to expand...

There are no other fuses only the main fuse close to the battery.
 
L.A.B. said:
There are no other fuses only the main fuse close to the battery.
Click to expand...

Not doubting you Les. If someone added those fuses before me they did a great job. Those crimps on the fuse terminals are factory perfect. I changed some wiring on the white but that blue/yellow is the same as when I bought the bike.
Pete
 
Deets55 said:
If someone added those fuses before me they did a great job. Those crimps on the fuse terminals are factory perfect. I changed some wiring on the white but that blue/yellow is the same as when I bought the bike.
Click to expand...

Well, nothing about any additional fuses in the manual as they would be lower rated than the main "35A" (blow) fuse.

None shown on the wiring diagram, only the main fuse.
https://www.oldbritts.com/17_066396.html

I've never seen any additional fuse holders in Mk3 headlamp harness sections, new or old, so that's all very strange.
https://andover-norton.co.uk/en/shop-details/20590
75 Commando / No Headlight or taillight


http://www.britishwiring.com/Norton-Commando-850cc-Mk3-Motorcycle-Headlamp-Wiri-p/mc116pp.htm

Do any other Mk3 owners have what appear to be factory fuses in their Mk3's headlamp shell?
 
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Thomas,
Those three fuse holders were on the bike when I bought somewhere around 1990-91. I installed the relays, solid state flasher, LED headlight and extra power tap behind the headlight shell. That all contributed to the birds nest in the shell. You can vaguely see the card inside the Lucas fuse in one of the fuse holders.
I agree with Les about none of the fuses showing up on the electrical diagram, trust me, when that white one blew when the bike was new to me it drove me crazy. PO did a nice job if he/her did the install. I only owned and worked on one Norton and it’s this one, so I can’t be certain about anything except it’s fun to ride and always keeps me busy. Especially in the early years. If it wasn’t for this forum and the great guys who contribute I would be spending more time pushing than riding.
Pete
 
The MkIII I used to have also had the fuses in the headlight. Definitely original wiring. I always thought it was odd that there was no mention in the manual or wiring diagram.
 
Ron L said:
The MkIII I used to have also had the fuses in the headlight. Definitely original wiring. I always thought it was odd that there was no mention in the manual or wiring diagram.
Click to expand...


Thanks for the input Ron. Do you recall the “production date” ? Mine is stamped Feb 1975, serial number puts it in the first 2,000 manufactured. I don’t recall off the top of my head the exact number. It shares a couple of items with the MK II that are different from the MKIII shop manual.
Pete
 
Yep, that’s it. Why is it that we save all that stuff ?
Thanks,
Pete
 
Deets55 said:
Not doubting you Les. If someone added those fuses before me they did a great job. Those crimps on the fuse terminals are factory perfect. I changed some wiring on the white but that blue/yellow is the same as when I bought the bike.
Pete
Click to expand...
Les is wrong.
 
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