850 MKIII Ignition Questions

Hi All,

I'm trying to sort the 1975 850 Commando I bought and see if I can get it running.

I'm a little confused with the iginition and there are some wires not connected. I have a wiring diagram, but I think it has an aftermarket ignition. Hope someone can help me figure this out.

When I picked up the bike the guy handed me this nice ignition plate with points and condensers:

http://www.flickr.com/photos/22794316@N03/8884426540/

At first I thought that was a spare, but then I found this label under the seat:

http://www.flickr.com/photos/22794316@N03/8884426618/

So I am assuming it has a Boyer ignition but haven't opened the cover to look yet. Problem is I can't find what they call the "black box" anywhere on the bike.

There is a bundle of wires by the battery that are taped of and this little electrical block:

http://www.flickr.com/photos/22794316@N03/8883808323/

Thinking this is an original Norton part...but not sure.

Any help appreciated.

The Boyer box is usually under the tank, in the frame crotch

You need to open up the points cover on the timing case - its the round dome shape one with 2 screws (one above one below) to see if it has a electronic pick up unit inside. The Boyer item has a pale yellow plastic back plate with 2 copper wire blocks mounted opposite each other. Coming off the backing plate are 2 soldered wires that connect to the original Yellow Black and White Black points wires. These usually run up a front frame tube to under the fuel tank near the head stock. The Boyer ignition box is black and about the size of small pack of cigarettes. It has white, red, and black wires along with the 2 ignition pick up wires.
The white goes into the Norton harness for power, the red is Positive Earth, the black power to the two 6Volt ignition coils.

Okay...whats that little box with the terminals on it...looks like it should be wired in...AL designation used to mean alternator in my day

Looks like the Boyer is all there...

Here's under the points cover:

http://www.flickr.com/photos/22794316@N03/8884200701/

Here's under the tank:

http://www.flickr.com/photos/22794316@N03/8884201233/

Wiring needs a little clean up...still wondering what this is:

http://www.flickr.com/photos/22794316@N03/8883808323/

Okay I sorted that out...it's the Warning Light Unit. All the wires are disconnected from that and taped off.

dennisgb said:

Okay...whats that little box with the terminals on it...looks like it should be wired in...AL designation used to mean alternator in my day

...

Click to expand...

That's what is typically called the assimilator box. It does connect to the electrical system. In simple terms it turns on/off the idiot light on the dashboard (by the key) depending on battery charging voltage.

lbridges said:

dennisgb said:

Okay...whats that little box with the terminals on it...looks like it should be wired in...AL designation used to mean alternator in my day

...

Click to expand...

That's what is typically called the assimilator box. It does connect to the electrical system. In simple terms it turns on/off the idiot light on the dashboard (by the key) depending on battery charging voltage.

Click to expand...

Yes sorted that on the wiring diagram (Warning Light Unit). All the wires are disconnected and taped...wonder why?

If the bike was changed to negative ground, then the box won't work. Alternately, it could have failed and the PO wired around it (all it does is determine if the idiot light comes on or not).

lbridges said:

If the bike was changed to negative ground, then the box won't work. Alternately, it could have failed and the PO wired around it (all it does is determine if the idiot light comes on or not).

Click to expand...

Is there a reason someone would change the ground? How would I tell if it has been changed? I'm hoping to put this bike back to original condition so would want proper ground and for everything to work.

dennisgb said:

When I picked up the bike the guy handed me this nice ignition plate with points and condensers:

http://www.flickr.com/photos/22794316@N03/8884426540/

Click to expand...

That points plate is from a Japanese bike.

lbridges said:

dennisgb said:

Okay...whats that little box with the terminals on it...looks like it should be wired in...AL designation used to mean alternator in my day

...

Click to expand...

That's what is typically called the assimilator box. It does connect to the electrical system. In simple terms it turns on/off the idiot light on the dashboard (by the key) depending on battery charging voltage.

Click to expand...

06-6392 is the Canadian model "automatic lights on" assimilator/warning light unit, so it isn't the normal on/off charge warning assimilator (06-6393) see MkIII manual, Section J8: http://britmoto.com/manuals/Manuals/850_man.pdf

dennisgb said:

Is there a reason someone would change the ground?

Click to expand...

It's usually done in order to fit modern electronics (satnav etc.) or LED bulbs, however some owners do it simply because they are more used to vehicles being negative earth/ground.

dennisgb said:

How would I tell if it has been changed?

Click to expand...

You could check the polarity of various electrical components such as the rectifier, Zener diode (x2 MkIII), Boyer box and coils. http://www.boyerbransden.com/pdf/KIT000 ... 00017_.pdf

L.A.B. said:

You could check the polarity of various electrical components such as the rectifier, Zener diode (x2 MkIII), Boyer box and coils.

Click to expand...

Okay, but the problem is there isn't a battery in the bike yet. Can't check polarity without a battery. What happens if I hook up the battery positive ground and it has been changed to negative ground. Is there a way to determine if it has been changed before I put a battery in it? Do they just switch the cables...that doesn't make sense to me because you would think it would fry stuff, but then these bikes are pretty simple electrically so maybe not.

dennisgb said:

L.A.B. said:

You could check the polarity of various electrical components such as the rectifier, Zener diode (x2 MkIII), Boyer box and coils.

Click to expand...

Okay, but the problem is there isn't a battery in the bike yet. Can't check polarity without a battery.

Click to expand...

Yes, you can, and you should.

dennisgb said:

What happens if I hook up the battery positive ground and it has been changed to negative ground. Is there a way to determine if it has been changed before I put a battery in it?

Click to expand...

I already explained how to do it by checking the polarity of the rectifier, Zeners and Boyer [Edit: also the 2MC capacitor-if fitted. The Zeners will not be so easy to check visually, so as long as the rectifier and Boyer box polarity can be determined then the Zeners are likely to be the same if connected.
Getting the battery connections wrong should at least blow the fuse immediately, but I wouldn't consider that a particularly good way of identifying polarity.]

dennisgb said:

Do they just switch the cables...that doesn't make sense to me because you would think it would fry stuff

Click to expand...

Precisely, which is why you need to check the items previously mentioned before installing a battery.

L.A.B. said:

Precisely, which is why you need to check the items previously mentioned before installing a battery.

Click to expand...

So I want to be careful here. In the body of what you wrote there is no description of how to go about actually doing the tests, just the components to check. Do I check the polarity to ground without power? Just make sure that the + side of everything is going to ground? Or should I go through the diagram and check everything? There isn't that much stuff on the bike so I can do that. Should I pull the connectors off the critical stuff before I hook up the battery? I can disconnect the Boyer, and any other stuff that could be damaged and work my way back on each...or I could just make sure everything that is supposed to be grounded is grounded + positive side.

dennisgb said:

L.A.B. said:

Precisely, which is why you need to check the items previously mentioned before installing a battery.

Click to expand...

So I want to be careful here. In the body of what you wrote there is no description of how to go about actually doing the tests, just the components to check. Do I check the polarity to ground without power? Just make sure that the + side of everything is going to ground?

Click to expand...

For the Boyer, simply check which box wire connects to the ground/frame side (use the Boyer diagram in the instruction sheet) if the electrical system is positive ground that should be the red Boyer box wire.

The "positive" side of the standard (2DV 406 = MkIII) rectifier is its mounting stud, so that will already be connected to ground if positive ground. The 2MC capacitor will also be connected so its positive terminal (the smallest one) is on the frame/ground side. The Zeners are usually marked for polarity , however they are not easy to check-but if the polarity of the previous items can be readily identified as being "positive side to ground" then the system is almost certainly positive ground.

dennisgb said:

Should I pull the connectors off the critical stuff before I hook up the battery?

Click to expand...

I will leave that up to you. If you are confident that the Boyer/coils, rectifier, 2MC are already connected with their positive wires/terminals to the ground side, then all should be well.

Is the electric starter operational (or intended to be)? If so, call back if you need any assistance connecting up the heavy gauge starter wiring and/or solenoid wiring. As it has a Boyer ignition the white/purple wire should already have been disconnected from the solenoid if the electric starter is intended to be operational (but I can't see it in the photos) if so, do not reconnect the white/purple to the solenoid.

L.A.B.

Thanks so much for the help. The starter is not there. There is a cover over the hole. I don't see much of the wiring there if any for the starter...I will sort that later. I see there are aftermarket replacement starters that are supposed to be better than the original, will look at whether that makes sense. It's one I need to think about given the small battery and whether to keep it stock...etc.