Wiring Harness...... smokem

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Surfdog

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Mar 1, 2010
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Ouch,
Got the new tires on.
Got the swingarm modified and bushed.
Got the clutch pull to a decent pull force.
Got the melted wiring harness........ Dang.

Yep the brown and blue wires, melted tape, insulation, down to the zener, up to the rectifier, inside the harness other wires too.
I got the diagram. But where do I start.
Have NOT determined the fault yet. Fuse did NOT blow. Might've been too large a rating.
Don't want to buy whole new harness. Should I?
Where/how do I find the where the short/fault was?
Is rectifier still good? Zener?
Thanks, and have pity on me. ha ha
You don't want to see pictures of this believe me.

Joe dog
 
I don't think a new harness is overly expensive. There is a guy making an aftermarket for stock replacement but for the life of me I can't remeber the business name.

You could make your own. Get a good regulator like a sparx unit and shit can all the zeners, ballast resistors ect and make one from scratch. It is not that hard.
 
Surfdog,

You've got to replace the harness, as you have no idea where the faults lie, and the condition of the other wires buried in the harness. If you have some mechanical ability, I urge you to build your own. Many schematics have appeared on this forum, and the harness is functionally simple; you can build it up on the bike and add stuff like a modern regulator/rectifier and fuse block. The only really tricky part is the collection of connectors in the headlight shell that require a pin removal tool (and pins) to reuse. As I recall, it took me 4 days to completely rewire my Mk3 to modern standards, with all harness parts provided by British Wiring. I posted my harness diagrams here a few months ago, which describe how the wires are grouped. If you're getting uncomfortable reading this, do as Dave suggests and buy one (you may need to replace the ignition harness as well as the main). The cost will be twice as much as buying the materials and doing it yourself; it's also not as much fun.
 
Thanks guys,
For the words of encouragement. And suggestions.
I was looking at replacing the main harness and have quotes coming from Britwire.
Rabers ranges from $189/taped to $259/cloth.
The ignition harness is different/separate from the main???
They seem all bundled together on my bike, and now melted together too. haha.

I solved a Smoking Wires problem on my BSA back a couple of years ago.
That was easy cuz it was only one wire and I could see what shorted, duh!

It could be easier for me now because my bike doesn't have blinkers or stock handle bar switches.
The wires for the indicators in the headlight are also taped off. And the assimilator was taken out by the PO.
It does have an older Boyer MarkII setup.
But who knows whats still working.
What should the amp rating on the main (only) fuse be??
I think there was a 30 in there. Zork!Zap.
I would hate to put in a new harness and have to kludge and clip such an expensive item.
or once its hooked up, have it melt again due to the faulty area is still in the system.

One thing.... I'm in no rush here.
And I realize nobody has a simple answer for me.
Although rewiring it myself seems cost effective, but pricing new ignition circuitry and installing it, I'm hesitant.

The dog is on an electrified fence.
 
$121 for the main harness from Old Britts. They are apparently backordered. I can ask Ella when I see them tomorrow when they think they'll get them in if you want.
 
Ok Yeah Swoosh,
Lemme know! When they expect em.
In reference to an earlier post in this thread:
Rick in seattle said: (you may need to replace the ignition harness as well as the main).
Is the "Ignition harness" different animal than the main harness? or is it all encompassing?
I think the wires to the ignition where the key is are ok.

Because my Blue/Brown wire is melted bare from Zener to Rectifier to inside the main rest of harness.
I guess I got the key off in time before the whole thing went up in smoke.

BZZZzzzzzz.
joe dog
 
Surfdog.

Before you get a wiring harness, you better find out what was causing the short. The brown /blue wire goes through jumpers, straight to the negative terminal of the battery. The other end is to the Master Switch # 1 terminal and then on to the accessory port. Better check the switch and the port, and all the wiring in-between. I would pull the wires from the switch and disconnect the port. Cut down the possibilities to one at a time by temporarily hand wiring past the switch. Do you remember if the key was in and what position it was at?

You might want to try to duplicate the problem before you invest the time and money in a harness.
 
Surfdog said:
What should the amp rating on the main (only) fuse be??
I think there was a 30 in there.
Click to expand...

30A blow? Or 30A continuous?


The original "35A" handbook/manual recommendation refers to the old British automotive blow amp rated fuses, rather than the now universally accepted continuous rating which is half the blow rating.
If the 1-1/4" 35A glass blow rated fuse has been replaced with any other type of 30A continuous rated fuse, it won't blow until 60A -which is far too high for the harness wiring!

Wiring Harness...... smokem
 
Surfdog,

Yes, the ignition harness is separate from the main harness; they are joined by the connectors located primarily in the headlight shell. The ignition harness services the handlebar control switches, lighting, horn, and ignition, so it carries substantial current. Pop the headlight out of the shell and take a look at what's behind it. If you have a Mk3, this is the time to upgrade the three heavy starter cables.

One huge advantage to building your harnesses is that you can build a sensible grounding scheme that does not depend on connections to the frame (excluding the coil secondaries and starter, of course) to function. The frame then becomes a redundant ground.
 
L.A.B. said:
If the 1-1/4" 35A glass blow rated fuse has been replaced with any other type of 30A continuous rated fuse, it won't blow until 60A -which is far too high for the harness wiring!
Click to expand...

Thanks for posting that bit of important information, Les. I didn't know that.

Surfdog — my Zener shorted out recently and blew the fuse. If it had been a higher rating than stock, the short circuit could have cooked the wiring harness. Maybe a shorted-out Zener could have been the cause of your meltdown? The manual tells you how to check it, but if you know someone with a spare, you could substitute it. Some forensic examination might put your mind at rest about how this started. Once I discovered the cause, my old rectifier was hurled into the bin along with the Zener, and was replaced by a modern Podtronics rectifier/regulator.

And by the way, how did you get a lighter clutch pull?
 
Coco said:
You could make your own. Get a good regulator like a sparx unit and shit can all the zeners, ballast resistors ect and make one from scratch. It is not that hard.
Click to expand...

it's actually quit easy if you have a volt meter + you learn a lot about the wiring - if your real bold just get a 50' spool of 14 gauge black wire from radio shack and have at it!
 
Hey guys,
Thanks for the constant info stream.
Here's my situation.
1972 Commando.
Previously cafe'd a bit.
No directionals, No stock handlebar switches or levers :^(.
I've had it for 2+ months and have been going at it furiously.
It was running pretty good it seemed.
The clutch pull was addressed by replacing the clutch loction circlip behind the clutch pack.
And tweaking the cable, lever and actuator adjustments.
Its by no means an easy pull but a bit better than before.
I did replace the headlight shell almost the first thing I did 2 months ago.
Very little wiring in there. All indicator wiring is taped off and wherever the assimilator was mounted before its not there now.
I believe the Ignition Switch wiring is external from the headlight now as the key switch itself is mounted on the top of the fork nut near the instruments.
I replaced the fiberglass tank with a steel pakistan tank in primer anticipating paint.
I got new tires and tubes to replace the 15 year old tires that were cracked and weathered badly about 2 weeks ago.
I subsequently noticed the handling seemed very sloppy when cornering.
My mechanic attacked the clutch pull problem and the swingarm bushing replacement last week when we discovered the nuts welded on the axis fix in place.
With the new bushings its much better and solid feeling.
Yesterday I took it out for another shake down run anticipating no problems and progressing towards breaking her down for paint maybe next week.
Just before meltdown, I noticed on higher revs she was like missing or slight sputter.
It got progressively worse until it just stopped.
I hopped off and saw the smoke and shut the key off.
Later yesterday as if by mental telepathy, Commando Specialties must have been reading the forum (I would if I was him), and posted a new taped harness on EBay. I bought it. It'll be here next week.
I would tackle the homebrewed wiring of the bike, but somehow it just seems this will be a bit easier.
I do have the Shop Manual and its has the wiring diagram. With all the color codes etc.
I've got the battery out, and both the rectifier and zener off the frame.
The brown/blue wires are melted and bare going to and from these devices. And have melted others by what seems just their proximity.
I will be testing both components anticipating replacing them. I will be examining the original harness for clues to the cause.
The fuse needs to be spec'd or the proper replacement looked up.
Thanks for the help and everything.
I hope I didn't miss anything in this description of the problem.
It reads a bit like a short story with a sad ending.
Joe dog
 
Update.....

Zener seems good?

Testing like this:

With the polarity one way resistance is about 10 ohms.
Switching the leads to the other polarity resistance is infinity.

I remember this procedure from decades past in the computer electronics industry.
Did I remember correctly or am I assuming too much?

Thanks
J dog
 
Surfdog said:
Zener seems good?
Click to expand...

Surfdog said:
I've got the battery out, and both the rectifier and zener off the frame.
The brown/blue wires are melted and bare going to and from these devices.
Click to expand...


I think the melted/burnt wiring is your biggest clue, as it shows the path of the short to ground from the battery.

If the brown/blue wire's insulation melted/burnt all the way to the Zener, then I'd think that it is very likely to be the cause of the problem, unless the wire shorted to ground at the Zener terminal, or at least very close to it?
 
just had it happen to me yesterday.The PO had separated the ignition system with a kill switch so i only had the lights on the key circuit. Was at a red light my buddy shouted shut off the bike!! Smoke all over. Flipped off the seat. Found the culprit electrical tape isolation and rode the bike for six more hours. I will call for a new lower harness Mon as I am riding again today. Any comments on the harnesses bought from these vendors mentioned?
 
Ok kids,
For those of you following along in the saga of burnt wires.
After a few hours of stripping and searching I think I found the origination point.
I disconnected all the components to the main harness.
Taillight, headlight, ignition switch, stator, and the electrical components, cap, rectifier, and Zener.
Tested the Zener it looks ok as in the earlier post.
Only the Zener and rectifier leads were melted.
The last thing I took off was the one thing i had put in just a couple of weeks ago or so.
I had made such a clean install, I thought it couldn't be that!
The Horn. I re-mounted the horn to the front of the battery box and had extended the wires so they could reach cleanly.
These butt splices I made were clean and insulated with shrink tubing and everything.
I mounted the horn so the wires and lugs were towards the center of the bike and had plenty of clearance.
Instead of facing the lugs of the horn straight down I had them turn to about 7 oclock position so they werent easily seen from the side or front of the bike. So clever. And instead of using tried and true approved covered/shielded female crimp-on lugs to make connection to the horn, I just used some automotive ones from Ace Hardare. They were bare and slipped onto the horn lugs ok.
Upon puilling the terminals which were hard to view, I reached down and started to gently yank them off. One of them felt funny. Crumbly and sharp. As i yanked a bit harder I heard a slight thunk and saw a washer fall to the floor. I looked at the leads and sure enough one was burned. I looked at the horn and that lug was discolored and the plastic insulating it from the body of the horn had a melted look. Closer inspection of the washer showed the black carbon of electric arching residue the matched the charred wire. The 7 oclock positioning of the horn terminals had allowed it to catch a wayward washer in flight. A small mark on the frame also coincided with where presumably it was wedged between the horn lug/wire. I tested the horn on the BSA. No honking.
Disappointment, yes at the melting of the harness, but the "aha! moment" of discovering the 95% potential cause of the failure was uplifting.
Now I can't wait for the harness to get here to clean up the rats nest of burnt wires and unused terminals.
Lessons learned here:
1. Always locate that dropped washer.
2. Never use unsheilded connectors on your electrics workmanship.
3. Persevere until you solve the riddle.
 
You had to ask that..!....
Well, I suspect while it was in the shop.
He had it for about 6 days. While we waited for the Clutch Locating Circlip.
It was mostly apart, and covered up while there.
I haven't worked on it in the 2 days interim since I got it back.
It ran ok coming home about 5 miles.
It coulda been me, fumble fingers, loosing and dropping items constantly.
It coulda been while in the shop too.
I can't tell for sure, but I'm going to absorb any grief that results.
Its a small island and an even smaller contingent of guys that would work on my ancient beast.
As long as I can get it rewired up and running, I should be almost done with it.
Ready for paint and pride of ownership along with running down the road, loud and fast.
J. dog
 
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