blue/yellow fried

headlight intermittent and no pilot led me to check headlight harness where i found the blue/yellow fried. ignition switch blue/yellow looks like it was overheated also. other than a direct short is there anything else that might have caused this?

also the main fuse didn't blow. it's a 35 amp. should it be a quick blow fuse or something similar? i'm not sure what this one is. thanks, rick

The orginal fuse would have been a 35 amp UK fuse which is the instananous blow rate, continuous blow rate is 17 Amp and is the modern way of rating, so fit a modern 20 amp or less fuse. Sounds like that has been the problem plus what caused the short which you still have to find, has someone fitted a 100W main bulb without a relay and separate feed.

Rick,

I believe your Commando is a '72 model, right? In which case I don't think there would normally be a Blue/Yellow wire in the '72 harness?

If I remember correctly, you had some problems getting the headlamp to work not that long ago, so how did you manage to fix that?

The pilot light should be on a separate circuit to the headlamp? They share the same ground from the headlamp but not the same feed?

Is there any possibility you could have connected the wiring to the headlamp bulb wrong so both filaments in the bulb are on at the same time? Or possibly one headlamp feed wire is shorting to the other bulb contact or feed wire, as that would probably overload the wiring having both bulb filaments on at once?

i rewired the main harness. it is a '72. there's a blue/yellow to one side of the selector switch on top of the headlamp shell and the 4 position on the ignition switch. i didn't change the headlight harness as the original looked good. my initial problem was trying to determine which was position 1 on the rear of the ignition switch. once i figured that out i got the headlight but lost the pilot and the tail light. brake light works. that's why i opened up the shell in the 1st place. when i got the bike the wiring was burned and all the handlebar pushbuttons were moved around.

i'm no electrician but i can do the basics. next move will be to install a new headlight harness, as i have one and cut open the tape on the main harness to see if it's going to ground or burnt up too.

Firstly , sorry, BLUE/YELLOW is correct for 1972-on, - I had been looking at the 1971 diagram!

rgrigutis said:

my initial problem was trying to determine which was position 1 on the rear of the ignition switch. once i figured that out i got the headlight but lost the pilot and the tail light.

Click to expand...

Which makes me think that maybe the ignition switch isn't wired correctly?

If it is an original Lucas switch then the terminal numbers should be stamped next to the terminals on the base of the switch, you will need good light and good eyesight to see the markings!

hello boys
i pulled the switch. it is white and says made in england. nos. 1,2,4 are marked. 1/brown-blue 2/white 3/brown-green 4/blue-yellow. when i connect it this way; in position 1all the way anticlockwise i get the headlight, brakelight, no taillight, no ignition, headlight turns off w/shell switch, key can be removed. 2nd position is dead, key can be removed. 3rd position ignition on, brakelight works. 4th position; pilot on, ignition on, brakelights work, no taillight. it's comepletely ass backwards from what it should be. taillight has worked previously so i may have inadvertently compromised it
while wrestling w/ the harness. that's for tommorrow as is the rest of it. it's better to walk away from it when you're frustrated. that's what homebrew is for.

8" of rain in 7 hours here today. no biking unless you mount your outriggers.

rgrigutis said:

when i connect it this way; in position 1all the way anticlockwise i get the headlight, brakelight, no taillight, no ignition, headlight turns off w/shell switch, key can be removed.

Click to expand...

That is the Parking lights position. So should be: Pilot/Tail/Instrument lights on, only.

rgrigutis said:

4th position; pilot on, ignition on, brakelights work, no taillight.

Click to expand...

= Ignition with lights
So the headlamp should also come on when the headlamp switch is turned on, and obviously there's a fault on the tail circuit? The instrument lights should be on?

thanks for the pic lab. that is not like my switch! i'll post a shot of it tommorrow. it's almost a relief to know that maybe i'm not going nuts w/ this and the switch is probably counterfeit.

I just replaced the switch on mine and sorted out the wiring. I suspect that either your switch is bad or your right handlebar switch/wiring is bad. From your description, it sounds like you have the tail light and brake light wires swapped in some way. Your switch should have four contacts and four switch positions. The wire connections that you indicate are correct. Fully counterclockwise should be parking lights as L.A.B. indicated. The next switch position should be the off position. The third position should be ignition on with with parking lights (no headlight); fourth position should be ignition on and headlight on. In the first, third and fourth positions your tail light should be on, not your brake light (hence my suspicion of your tail light wires).

The over-current in the blue/yellow wire indicates a short of some sort or a very high wattage headlamp bulb as someone else mentioned. If I was certain that I had the correct bulb and positive that both elements were not getting power at the same time, I'd be suspicious of the right handlebar switch and would examine it for indications of a short to ground or abraded wires.

By the way, if you go to Oldbritts.com, click on the 1972 link on the left, select basic electrical components, then click on item 21 for the ignition switch, you'll see a nice writeup on the proper ignition switch with nice pictures.

According to a 1972 Norton workshop manual, section J10, switch pos. 1=parking lights, pos. 2=off, pos.3=ignition only, pos. 4=ignition and lights. When I restored my 72 Combat I replaced the wiring harness with a stock replacement and I ended up with the same sequence as the manual. I would mention with positions 3 and 4 the brake light should work. I did change mine to have a headlight on in position 3, as well as position 4.

the switch depicted on old britts is different from mine. i see that the connectione are 1,3,2,4. mine is white and connections are1,2,3,4. talked to the guy at klemphs and he said the white switch like mine is reported to be a mystery to wire and is not of hi quality. i'm going to try to connect my white switch/ the lucas connections if that makes any sense.

With an Ohmmeter you could meter out the proper positions for your switch. I would start with the assumption that position 1 is the feed from the battery and go from there, measuring which posts are continuous at different key positions.

ok. the light came on, no pun intended, and i taught myself how to check the switch via ohmeter.

switch all the way anticlockwise; position 1 is connected to 4
1 click clockwise; dead
2 clicks clockwise; 1 is connected to 2
3 clicks clockwise; 1 is connected to 2 and 3

i know it's not right but what should it be? new switches are ungodly pricey, almpst like they're stamped aviation or maritime.

thanks, rick

rgrigutis said:

switch all the way anticlockwise; position 1 is connected to 4
1 click clockwise; dead
2 clicks clockwise; 1 is connected to 2
3 clicks clockwise; 1 is connected to 2 and 3

Click to expand...

Terminal numbers 3 and 4 on your switch are swapped around. So regard 3 as being 4, and 4 as being 3.

Even once the switch is correctly wired, this may not cure the headlamp problem, or lack of tail light?

By the way on a '72, in park position on the ignition switch the headlight will light when throwing the switch at the headlight.

illf8ed said:

By the way on a '72, in park position on the ignition switch the headlight will light when throwing the switch at the headlight.

Click to expand...

That would be true of the pre-'72 models, but 72-on shouldn't, unless there was some overlap of the '71 wiring used into '72?

As the separate headlamp wire (Blue/Yellow for '72) circuit should only connect to Ign./Sw. terminal 4, for '72-on?

Check the Blue/Yellow wire (UY) from Ign.Sw. terminal 4 in the 1972 diagram:
http://rocbo.lautre.net/technique/norto ... p/151.html

Terminal 1 (bat.), and headlamp terminal 4 (terminal 3 on Ricks!) of the Ign. switch as we know, are not common when the key is at the "parking lights" position so the headlamp shouldn't work at "parking lights".

For pre-'72 there is no terminal 4 on the switch, so the headlamp is connected in with the rest of the lighting circuit and can be switched on at "parking lights", which is, I believe why they changed the arrangement on the '72-on models?
http://rocbo.lautre.net/technique/norto ... p/150.html

you the man lab! that did the trick. everything works as it should except no taillight in position 4 altho i do get tail light in position 1. ??????????? you saved me a 100+ man. many thanks! thanks to everybody.

one more question while i'm on a roll. how do i wire pilot light to switch on in position 3 and 4? do i run a separate switch to ignition wire? i've a halogen pilot bulb for daylight riding.

today is starting out well. rick

OK Rick, well it's good to know you've got it (mostly!) sorted.

If, as you say, the tail lamp is coming on at switch key position 1 (park lights) then it should also come on at Sw/pos. 4? As the tail light circuit should be powered from the same switch terminal, and by the same wire, that's Ter.3 on the diagram, (but Ter.4 on your switch) so you should have a single Brown/Green wire from the Ign./Sw. to the tail lamp (as shown in the '72 wiring diagram)?

If you want the pilot to work at key Pos. 3 & 4, then disconnect it from Brown/Green circuit and connect it to any White wire.

But note that you will lose the pilot light for parking, unless you add another switch, if you attempted to wire the pilot to both Brown/Green and White circuits without an additional switch, then the White (ignition/brake light etc.) circuit would become hot when the key was turned to the parking lights position (1).