Blown fuse 73 Roadster

[Snortin Vache]

Hello,

I rewired my 73 Roadster last year from Grant Tiller/Greg Marsh's write-up and wiring diagram. This late winter/spring I have had problems blowing the fuse on my bike. The last couple times it has blown within 30 seconds after replacing it and starting up, and then most recently without even riding the bike, just replacing the fuse and fiddling with the key switch, which is a new Norton switch.

Anyway, I have dug into the problem a little bit, after wasting a couple of glass fuses from Britishwiring. I started with the key switch, which I disconnected everything from and set my meter to continuity to check that I understood the logic of the different positions. Everything worked as it should. Then I reconnected the negative feed to the key switch, with a new fuse in line, and once again, everything still operated as it should. But, when I added in the taillight wire to the key switch, the brown/green wire that feeds the taillight and instruments, I suddenly have continuity between all the poles on the key switch regardless of its position, i.e., iginition, ignition with lights, off, parking lights, or key completely removed from the switch. Not my instrument lights (new harnesses and bulbs), nor my taillight (old bulb) were lit up, and my battery is at a steady 12.3 volts when I check it with the meter. I should also add that the key switch was hooked up for weeks in this state with no battery tender and the battery has remained solid (new AMG battery).

My electrical knowledge and capabilities have allowed me to rewire my bike, but evidently, not sufficiently well, so I would appreciate some guidance. I am going to examine the bulbs and wires in this circuit, but if someone with some electrical sense could tell me what is going on or a more refined procedure for diagnosing this problem I would appreciate it.

Cheers to spring in the northern hemisphere

 

[concours]

"New" does not always equal good.

Scrutinize the switch.

 

[L.A.B.]

But, when I added in the taillight wire to the key switch, the brown/green wire that feeds the taillight and instruments, I suddenly have continuity between all the poles on the key switch regardless of its position, i.e., iginition, ignition with lights, off, parking lights, or key completely removed from the switch.

Surely the continuity must have been there before you added the brown/green wire to the switch (terminal 3) if the switch is faulty, or I do not understand this.

 

[Snortin Vache]

Surely the continuity must have been there before you added the brown/green wire to the switch (terminal 3) if the switch is faulty, or I do not understand this.

Let me try to clarify. What I meant to say is that with everything unplugged from the key switch, I get continuity between the correct terminals with respect to the key position. I.e., One position clockwise gets a common set of spades to have continuity (my white ignition wires). Two positions clockwise gets the two whites plus another set of common spades (blue/yellow two position headlight wire and brown/green taillight/instruments) and one position anticlockwise from off gets just the common spades with blue/yellow and brown/green for my parking lights. All of this checks out with nothing plugged in with my multimeter.

Then, added the negative feed brown/blue to the key switch. Still the key switch functions as I think it should in all 4 positions, including off. But, when I add the tail light brown/green to its terminal; which previously was only common with the negative feed in two positions (ignition plus lights (two clockwise) or parking lights (one anticlockwise); now all the terminals of the key switch have continuity with all the other terminals in all positions.

 

[L.A.B.]

and one position anticlockwise from off gets just the common spades with blue/yellow and brown/green for my parking lights.

Blue/yellow (at terminal 4) shouldn't be hot at the parking lights position. The headlamp pilot light is fed by brown/green.

 

[Snortin Vache]

Blue/yellow (at terminal 4) shouldn't be hot at the parking lights position. The headlamp pilot light is fed by brown/green.

Ok, I understand. I do not think it has anything to do with my problem, but I would like to learn how the key switch is supposed to operate. Honestly the terminal positions are less helpful for me as it is difficult to see them on the switch, and on my wiring diagram the terminals do not inform the logic of the different key positions, as far as I know.

So, simply put, I have a brown/blue from the negative terminal of the battery. Two whites. A blue/yellow that goes to the two position switch on my headlight. And a brown/green that goes to my instrument lights and my taillight.

With this there are four key positions, including off. At the off position, the brown/blue must go on a terminal that is not common with any other terminal.

From there, maybe you can clarify the other three positions and where my wires should be hooked up.

 

[L.A.B.]

From there, maybe you can clarify the other three positions and where my wires should be hooked up.

 

[marshg246]

Ok, I understand. I do not think it has anything to do with my problem, but I would like to learn how the key switch is supposed to operate. Honestly the terminal positions are less helpful for me as it is difficult to see them on the switch, and on my wiring diagram the terminals do not inform the logic of the different key positions, as far as I know.

So, simply put, I have a brown/blue from the negative terminal of the battery. Two whites. A blue/yellow that goes to the two position switch on my headlight. And a brown/green that goes to my instrument lights and my taillight.

With this there are four key positions, including off. At the off position, the brown/blue must go on a terminal that is not common with any other terminal.

From there, maybe you can clarify the other three positions and where my wires should be hooked up.

All the way counterclockwise, terminals 1 & 3 are connected
On click clockwise, Off, none are connected
One click clockwise from off, 1 & 2 are connected
Two clicks clockwise from off, all are connected.

See the picture L.A.B provided - this is just re-stating what he already showed.

Brown/Blue Terminal 1
White(s) Terminal 2
Brown/Green Terminal 3
Blue/Yellow Terminal 4

With wires connected to the switch you should not be checking continuity - will just confuse you.

 

[L.A.B.]

One slight peculiarity of the standard switch is that terminals 2 and 3 are connected at OFF, although this seems to serve no purpose; it is just a peculiarity of the switch design.