Melting Wire

The wire that holds the master fuse that attaches to the negative battery terminal has been showing signs of heat, up to the point where the insullation has melted. In addition, last night the bike would not run unless it was held to a high idle, would hic-cup when changing between high and low beam, and not want to idle.

Prior to the bike acting up (later in the day) it had been running fine. No starting issues, no running problems, notta. Now I am more than a bit confused.

It is a 1973, 750, Boyer ignition, Single Mikuni. Has had a total rebuild within the last three years.

Bad connection and or the wire breaking down causing high resistance perhaps.

Cash

What size fuse are you using? Sounds like something is drawing a lot of current. Measure your voltage while running engine at different speeds and let us know the voltages you get.

What is this electronics issue week?

Dave
69S

Ya I would think either there is a "resistive short" causing too much current or bad connection's. Fuse should blow if its sized correctly...But forsure if you could messure the voltage and current and turn different things on and off maybe you can figure it out? Zenier?? (thats really random)

I had the same problem. All the ground wires were frying.
Make sure the battery is being held down and not getting bounced around or if it is held down make sure the hold down is not shorting.
Also check in the headlight shell for any wires that may have come loose.
The fuse should be 35amps. I run a 30 amp cuz it's all I can get without ordering it from a Norton parts guy.

My problem was I had no hold down, no fuse and wires in the headlight shell were just flopping around. Idiot, right? Right!

I now have a new harness and all is well.
If you fried your wires and your harness is just old and nasty it would be a good idea to get a new one as melted wires can expose wire to wire.

I sure have been posting a lot this weekend.
Time to go for a ride.

You have a dead short they are easy to find. You only need to put a light bulb in between the battery and the negative wire. With the key off- no light what so ever should come to the bulb. When the key is turned on it may flash for just a moment than turn off Boyer turning on than off when it gets no input. If the light stays on does a tail light always light up when key is on? Unhook it. Light still on? What ease turns on with the key? Kill switch? Than a Boyer but that load goes away as soon the Boyer shuts off. Is the horn wire or its relay stuck on? Brake light switch stuck on? Head light switch stuck on or are the bright dim switch corroded inside the handlebar switch? A load that causes heat will so as a light in the bulb take out one thing at a time till the light goes out there’s your short.

batery-fuse-t4233.html

After you find the cause of the short you might want to go to a 15-20amp fuse. The old rating system that was used in the shop manual was "blow point".
Modern fuses are rated at their continuous capacity. Apparently, there's a difference of almost 2:1 Wouldn't do anything to prevent the short but it would prevent the insulation getting cooked.

Guido said:

The fuse should be 35amps. I run a 30 amp cuz it's all I can get without ordering it from a Norton parts guy.

Click to expand...

As rpatton has said, "35A" refers to the blow rating of the old British 1-1/4" glass fuses.
If that type of fuse is replaced with another, then it should be approximately half the rating-even if it's the 1" glass fuse type.

Additional information:

1) Has a 30 AMP modern fuse. (Blade type)

2) Wiring harness was replaced with new one when rebuild was done.

3) I am suspecting bad connection at the splice and at the battery.

4) Larger (lower gauge) wire spliced to smaller diameter wire that then connects to battery.

5) I will replace the 30 AMP fuse with a 20 AMP


Plan: Find a correct size connector that I will then solder to the larger wire, attaching it directly to the battery, eliminating the butt connector splice. Now all I need to do is find the type of ring connector I am looking for. One that ia not a pinch connection, but one where you make a good mechanical connection, then solder it to ensure a correct electrical connection.

Your opinions on my proposed fix will be appreciated.

Thanks.

That's a start ,but you still have a slow resistive short that must be traced and rectified.

A few years ago I went for a 300 mile ride and stayed overnight in a van park. Went to my bike the following morning to find some of the harnass burnt out and a flat battery. I had fitted a 35 amp continuous fuse instead of a 20 amp. The double rating in the Norton manual is confusing. I cut some good wire out of the harnass and spliced it in to give me ignition and the capacitor enabled the bike to start on about the third kick. I took of but after about 10 miles the bike cut out. I checked spark and fuel and then the bike restarted again but stopped again after about 10 miles. the bike probably did this 4 or 5 times until I realised the battery had boiled. When I looked at the charging system a little closer I realised as I tightened it the zener diode it had spun a little and the spade electrical fitting had touched the frame. It worked ok like that for probably a year until the plastic cover on the spade fitting rubbed through. A short. I moved the electrical connection away from the frame and rode the bike the remaining 250 miles home without a problem. The moral, dont fit too big a fuse and look for a short in the strangest places. hope you find the problem.
ando

Trapped wire , flattened and split . SOMEWHERE .oh bother . Look for flattening / chaffing / rubbing .

Grabbing a handfull somewhere and heaving to get slack couldve taughtened it elsewhere , if you recall
itd help locate. Otherwise internal dislocation / disentigration of Component ' somewhere ' .

A good long relaxed hunt along the lot , tank seat & covers off . Id suspect handlebar switch gear .
Any contraption used in the rain particularly can do with a good dose of C.R.C. waterproofing occasionally .
( Squirting inside the switch blocks . Dont believe it . Can hose out alternators on cars if sprayed inside,gets rid of the dust )

Particularly british ones parked outdoors overnight at times . Often impedance from dirty contacts is 90 $ of electrical
maladys , Initialy .The sum of its parts. It quite a simple machine , theres only a few thousand off them . :shock: 8)

Guido said:

I had the same problem. All the ground wires were frying.
Make sure the battery is being held down and not getting bounced around or if it is held down make sure the hold down is not shorting.
Also check in the headlight shell for any wires that may have come loose.
The fuse should be 35amps. I run a 30 amp cuz it's all I can get without ordering it from a Norton parts guy.

My problem was I had no hold down, no fuse and wires in the headlight shell were just flopping around. Idiot, right? Right!

I now have a new harness and all is well.
If you fried your wires and your harness is just old and nasty it would be a good idea to get a new one as melted wires can expose wire to wire.

I sure have been posting a lot this weekend.
Time to go for a ride.

Click to expand...

Suggestions which harness to get ? I have also experienced melting (and more than melting...), and changing the harness is the next thing I wanna focus on.

Make your own the way YOU want it to be.

Ordo , a Mk 4 Zepher has ebnough wire to do a aircraft carrier with . Hillman Hunters seem to have good terminals / connectors . All English stuff before 74 unless M4 cortina has Std. british colour codes .All the wires in the cabin are usually A1, though strip a few or dicard any you find the notorious blackening of core in .Grab a pkt of small two dollar shop cable tyes as assitt locateing wires whilst looming .

ANY old car manual will have SAME colour per purpose , H & L beam , switch , Wng . Oil , Alt etc . No Worries .

Silly TRAILER Lead Wire is lighter but still high ? capacity . ( Some Mk4 Z car mains ( Br) are 1/8 dia. core . :shock: )

You can throw in a pile of relays ' borrowed ' from a 80s car for Lamps and Air Horn etc , so as to not have high current
through delicate switch contacts .

If you do seperate , or seperate into , IGNITION / Engine ; Lighting / Aux ; CHARGEING ; & interior ! its Logical .
seperate sub circuits , i.e. inst lighting . Starting at the furthest ends from battery , and pulling arount to correct lengths before tapeing with tested ( for sticking , & to itself ) quality insulateing tape & maybe shrink wrap .

Rally car logic to system gives trouble free diagnostics . Leave enough for bar swing and detouring around to avoid trapping.

dont use cheap solder either. The fittings from cars are utilised as is and salvaged where nesseary .Most dismantleable with pointy pliers , blade and iron , Have a damp thingo to wet burnt fingers & cool of bits quick .

thanks folks, that helps, although I might look for a ready made solution. I have NO electric skills whatsoever...

steveyacht said:

Additional information:

1) Has a 30 AMP modern fuse. (Blade type)

2) Wiring harness was replaced with new one when rebuild was done.

3) I am suspecting bad connection at the splice and at the battery.

4) Larger (lower gauge) wire spliced to smaller diameter wire that then connects to battery.

5) I will replace the 30 AMP fuse with a 20 AMP


Plan: Find a correct size connector that I will then solder to the larger wire, attaching it directly to the battery, eliminating the butt connector splice. Now all I need to do is find the type of ring connector I am looking for. One that ia not a pinch connection, but one where you make a good mechanical connection, then solder it to ensure a correct electrical connection.

Your opinions on my proposed fix will be appreciated.

Thanks.

Click to expand...

Found bad connection on battery to the fuse wire. Cut it and sliced on a new ring connectior with solder and mechanical connection. Have heavier gauge wire feeding smaller wire in harness now. Changed inline fuse to a 20 amp unit as suggested. Will be going on an extended ride this weekend to see how it all works out.

PS: No other shorts or electical faults found with test light or multi meter looking for voltage drops.

Either you have been very lucky or there has been a deeper problem. I would suggest that you disconnect the reg/rec from battery & check when connected 7 disconnected there is no problem. Also check when engine is running that there is around 15 volts going into the battery.

Bernhard said:

Either you have been very lucky or there has been a deeper problem. I would suggest that you disconnect the reg/rec from battery & check when connected 7 disconnected there is no problem. Also check when engine is running that there is around 15 volts going into the battery.

Click to expand...

I will do as you suggest, thank you. One thing I forgot to mention is that the battery was not secured nearly as sound as I would like. I will be rigging some additional tie downs prior to going for a ride this weekend. Sure wish there were a better way to secure battery than with a bunch of zip ties, bubble gum and bailing wire.

Capacitor shorting out? There is another thread active on that topic.