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Melted positive ground wire T100C #797867 02/08/20 4:15 pm
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vintage rider Offline OP
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I will try to make this as detailed as I can. 1968 T100C, positive ground. I tore bike down and built back up. Original wiring harness was toast, so I ordered one off internet some years ago. Finally got around to installing the harness, and spent many days and nights making sure that everything worked, including sparkplugs, etc. One thing I noticed was that the battery was draining with the motorcycle just sitting there (I had not started the thing yet, as I was working on restoring the tank). After a month of reading and troubleshooting, I determined the Zener diode was draining off voltage when it should not have been. I replaced it and the rectifier with a positive ground tympanium unit. Battery seemed to be holding a charge after that.

However, I went ahead and disconnected the negative wire from the battery and hooked up a trickle charger to the battery to maintain a charge, the positive wire was still hooked up from the frame to the positive post of the battery.

I finally finished the tank and was installing it when I noticed the negative (black) wire coming from the trickle charge to the battery had the insulation melted in one spot. Upon further examination, I found that ONE positive red wire going from the grounding lug installed at the battery box had melted insulation from the grounding lug all the way along the wiring harness to the grounding lug below where the Zener diode has been installed ( I had removed the wire from the Zener diode according to the tympanium directions, but left the diode there for aesthetics, and obviously the red wires that attached to the lug that attached the Zener diode to the bike.

Needless to say, at that point, I was confused. My electrical understanding is somewhere between tackling the wire harness install and hoping nothing goes wrong. I dug out the old wiring harness just to verify what I was seeing on the bike…and lo and behold, (I never took a good look at the old wiring harness before I removed it) the same red wire going from the battery area to where it would have been attached to the lug where the Zener diode was installed was melted as well! When I purchased this bike, I had made sure it started, which it did. I ran it for a couple minutes, then turned it off and tore it down. It ran, that’s all I knew.

I am at a loss, and as stated, my electrical skills stop when electrical issues like this occur. I have ordered a new harness, but I have to determine what is going on before ever installing it. I did see something on one of the websites for britbikes about making sure there is a good ground, and when I did a continuity test of the ground lug at the battery box, it is showing something like 12 megohms of resistance, not what I figured I would see.

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Re: Melted positive ground wire T100C [Re: vintage rider] #797872 02/08/20 5:18 pm
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What was the current of the trickle charger? Hopefully not an auto trickle charger which usually runs about 2 Amps.
Without a connection from the negative side of the trickle charger to the harness the melted harness wire was not from the charger.
I suspect the zener was shorted which melted the original wire and when you put in the new harness and were testing you melted the wire in the new harness.
The high resistance from the battery box ground was to where? the frame or engine?
The "ground lug at the battery box" meaning the red ground wire that goes to the battery?

Re: Melted positive ground wire T100C [Re: vintage rider] #797877 02/08/20 6:00 pm
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Just to clarify a few bits of your post:

When you say " I determined the Zener diode was draining off voltage when it should not have been. I replaced it and the rectifier with a positive ground tympanium unit. Battery seemed to be holding a charge after that."
did you actually check that the battery held its charge over a similar amount of time during which the presumed faulty Zener would have discharged it?

There is a correct fuse (15 to 20A continuous rating) installed, presumably near to the battery -ve?

The +ve and -ve wires of the Typanium connect to where?

Was the saddle installed at all when you were testing the functioning of the new harness?

"disconnected the negative wire from the battery and hooked up a trickle charger to the battery to maintain a charge, the positive wire was still hooked up from the frame to the positive post of the battery."
Since doing this, while the charger was connected (directly to the battery terminal posts I assume?) the harness battery wire has been kept totally isolated from the battery -ve post?

The terminal of the Brown/Blue wire that originally fed the Zener is well-isolated with tape, or the wire removed entirely?

When you say "when I did a continuity test of the ground lug at the battery box, it is showing something like 12 megohms of resistance"
what exactly were you contacting with the meter probes?

Until you can clarify these points, my provisional thoughts are as folows:

I'm doubtful that your melted red harness lead happened while the -ve battery terminal was disconnected from the harness (I don't see a way that it could).
I think this must have happened with the battery fully connected to the harness, while testing during harness installation.
As you haven't got to the stage of starting the bike since beginning the refurb, such current can only have come from the battery.
The trickle charger wires should be rather fine in comparison with the melted red wire. In the bizarre circumstance (that I cannot imagine at the moment) that the red-wire melting current derived from the charger, I would expect the charger wires to show extensive melting, not just in one place. The dmage being so localized suggests that the charger wire rested at some time on a wire that was getting hot.
It is definitely a motorcycle trickle-charger? delivering only fractions of an amp?

Re: Melted positive ground wire T100C [Re: vintage rider] #797913 02/09/20 12:04 am
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vintage rider Offline OP
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The Zener diode was not plugged in. Plug was taped and not in contact with the Zener or frame.

Using a 4 amp charger that simply maintains battery voltage when battery drops below a certain voltage. The battery was hooked up for an extended period of time while I was getting everything (points, lights, etc) to work, and I would have noticed the red ground wire starting to melt.

After determining the Zener was drawing the battery down, and installing the tympanium regulator/rectifier assembly, the battery maintained it's charge after that. The Tympanium is a positive ground. I double checked. And it is installed per the directions.

The seat has never been on the motorcycle since I started this project. It would not have been a source of grounding.

I used a multimeter to determine a large amount of resistance between the lug that is bolted to the battery box (I assumed this is where the old red positive grounds were attached) and the frame of the motorcycle.

The lug where the Zener was installed and where the red wires were attached is completely clean of paint.

There was no way the black wire coming from the charger ever came in contact with the red ground wires or any other wires. It was however draped over the side of the frame. I assume the wire was in good shape and not frayed.

And, as I stated, when I looked at the old wiring harness, the same red ground wire was melted from where it had attached to the bike near the battery and the lug that bolts the Zener diode to the frame. So that tells me that the Zener, nor the tympanium regulator/rectifier are not likely culprits to the melting issue.

Re: Melted positive ground wire T100C [Re: vintage rider] #797925 02/09/20 5:07 am
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The Tympanium that I have has no polarity, two yellow wires, a black and red. The case is floating. Ground is which ever way you hook it up.
I use a 150ma wallwart to keep the RSVR1000 lead-acid battery topped. My auto charger is a Sears 10/2 amp but would not leave it connected for hours after the battery is topped up. Even on 2 amp it will heat up a car battery. On a discharged battery it will put out more than 2 amperes.
I am not familiar with the T100. Triples and twins have rubber buffers isolating the battery holder from the frame. So there you would get infinite resistance.
The battery is the only current source on the bike that can melt the wire.

Re: Melted positive ground wire T100C [Re: vintage rider] #797945 02/09/20 6:55 am
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Check seat can't short on battery live negative especially when rider seated. I recall this happening many years ago but can't remember details except it puzzled rider for some time. Check seat rubber buffers, battery installed height and the like. Good luck.

Re: Melted positive ground wire T100C [Re: vintage rider] #798008 02/09/20 10:01 pm
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koan58 Offline
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Thanks for your replies.
Just re-asking a couple of questions , as you missed them out in your reply.

There is a correct fuse (15 to 20A continuous rating) installed, presumably near to the battery -ve?
AND if so, the fuse has not blown at any time during installation of the new harness?

The +ve and -ve wires of the Typanium connect to where?

When you say "when I did a continuity test of the ground lug at the battery box, it is showing something like 12 megohms of resistance" it would be more relevant to check for resistance between the "ground lug" (where presumably all the red wires collect) and the battery +ve terminal, as this is where they need to get to.


A good place to create the red wire gathering place is often where the rectifier was mounted.


I'm wondering if you're present arrangement is relying on ground return to the battery via the red wires from the Zener, rather than a more direct route.
As that red wire is melted, I expect you'll be chopping it out anyway.
Then check resistance between gound lug and battery +ve. There should be a direct wire between these points anyway (a good idea to place the main fuse here rather than the -ve wire, but don't worry about that for the moment).
The resistance between any red wire connector and the battery +ve terminal should be very low, well under an ohm.

Even though your charger seems higher amperage than what I would call a trickle charger, I don't see how it has anything to do with the wire melting.

As DMadigan said, only when the battery was hooked up to the bike could there have been sufficient current to melt that wire.
I suspect that happened when the Zener was still present, even though you may not have noticed it at the time.


The ground wire for the Zener is probably fairly moderate duty (in terms of amps), so it may be that with a failed Zener perhaps allowing 15-20A it could allow melting of a wire rated for more modest amps without blowing the fuse.
I'm rather clutching at straws here, as I would expect you to have noticed the battery losing charge rapidly (say within 30 minutes),


It is a tough one to explain, for sure!

Re: Melted positive ground wire T100C [Re: vintage rider] #798045 02/10/20 5:43 pm
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vintage rider Offline OP
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Thanks for all the tips! Appreciate it. I was hoping somebody had the same issue at one time and knew what the issue was. In any case, I am turning into a T100C wiring expert...at far as where all the wires go and what they do.

Yes, there was a 20 amp fuse installed, and no, it was not blown. The wires from the tympanium connect to the two wires that originally were installed at the rectifier. The brown wire goes to the battery, and the red goes to the grounding lug near the battery.

I am going to ensure when the new harness is installed (already started and THAT creates another issue) that the red wires are grounded at a point that ensure no resistance between them and the frame of the motorcycle.

I am going to install the harness, hook up the battery, and then watch to see if the red wire going to the lug where the Zener is mounted to the bike starts to heat up.

However, as stated above, when I was started to un-install the old harness and reinstall the new harness, I noticed that the two small bulb holders that are pushed into the red and green warning light indicators in the headlight shell are NOT the same as the ones on the installed harness, and will not accept the 2 watt bulbs presently installed. I have no idea what type of bulb would be used in these new bulb holders. The rest of the wiring harness looks to be correct.

Re: Melted positive ground wire T100C [Re: vintage rider] #798056 02/10/20 7:53 pm
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A harness for your year of bike should have red ground return wires for almost all of the systems on the bike, such that the frame is not required as an electrical path.

Keep in mind that ground return doesn't mean a connection to the frame, but a very low resistance connection between the +ve terminal of any consumer (bulb etc) and battery +ve. This should be done by red wires in most cases.

The only exceptions are the ignition system, which requires a ground return for the contact breakers and sparkplugs. This is best served by a dedicated lead from your common grounding point (often called a SPG or single point ground) to an engine bolt (often on the head steady).
Your harness may or may not have a ground return from the rear light unit. If it hasn't you'd be well advised to install one.

There is an article I've seen about SPG by RFWhatley under GABMA on here somewhere, damned if I can find it now! Perhaps someone will help?

If you choose your SPG (where you clamp all your +ve leads to) to be the original rectifier mounting, just clean the surfaces, clamp all the ring terminals together and slather it with vaseline/grease.
This will also give a ground to the frame (belt and braces, not strictly essential).

All the +ve wires should come together at that SPG, including the engine ground mentioned above, the +ve of the Tympanium and of course a wire to the battery +ve terminal.
The wire to the battery +ve is a better place to put a main fuse (harking back to questions about the saddle, it can cause a short which a fuse in the -ve lead doesn't protect against).

"I am going to install the harness, hook up the battery, and then watch to see if the red wire going to the lug where the Zener is mounted to the bike starts to heat up."
It shouldn't have anything to do with anything, unless by some peculiar grounding arrangement it has become the principal return for the whole system.

I'd suggest soldering wires to the side and end of a 12V bulb and substituting it for your fuse. Then if a similar whatever shorting situation arises, the bulb will glimmer as an indication, and will also limit the current so as to cause no damage.

I don't lnow what your standard idiot lamp bulb holders would be, or what the options are. Stuart is likely the one for that.
At worst, if you're handy with a soldering iron, you could swap them for the old ones?

Good luck!

Re: Melted positive ground wire T100C [Re: vintage rider] #798062 02/10/20 9:44 pm
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https://gabma.us/tech-articles/

20 amp fuse is way to big. Get rid of the glass fuse and put in a blade type fuse. 10 / 15 is plenty.
A battery tender of 750 ma is about right for these bikes. I have have a 750ma and a 1 1/2 amp.

Last edited by desco; 02/10/20 9:46 pm.

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Any advice given is without a warranty expressed or implied.
Re: Melted positive ground wire T100C [Re: vintage rider] #798064 02/10/20 10:04 pm
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Re: Melted positive ground wire T100C [Re: vintage rider] #798146 02/12/20 1:25 am
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"Yes, there was a 20 amp fuse installed, and no, it was not blown. The wires from the tympanium connect to the two wires that originally were installed at the rectifier. The brown wire goes to the battery, and the red goes to the grounding lug near the battery."

Fuse installed where? If it's along the negative between the battery and the power switch, and the tympanium is connected directly to the battery, you are not protecting against current leakage through the tympanium. Although this is not the way the factory harness is fused, I have my fuse in the positive battery lead, between the battery and the grounding lug. Then there's no way current can flow from the battery without going through that fuse.

"I am going to install the harness, hook up the battery, and then watch to see if the red wire going to the lug where the Zener is mounted to the bike starts to heat up."

If you have a Tympanium, why do you still have a zener mounted? You don't need it, and should not have one. If the zener is hooked up, and is leaking current, this could be the whole problem, which would explain why it happened both before and after the installation of the Tympaium.

I agree a 20-amp fuse is too big. 15 amp is sufficient.


Mark Z

'65(lower)/'66(upper, wheels, front end, controls)/'67(seat, exhaust, fuel tank, headlamp)/'70(frame) A65 Bitsa.
Re: Melted positive ground wire T100C [Re: vintage rider] #798161 02/12/20 7:06 am
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Hi guys, On a side note, ohm meter is not very useful for testing connections or wires. All strands of wire except one could be broken & ohm meter will show perfect. Volt drop circuit under load is the real test. I'll often use a 21w bulb for load on small circuits. A headlamp bulb 40w on large circuits. Generally .2v drop is max. But each switch like ignition, stop lamp etc. Might/will drop .2v, add the double bullet connectors along the way, & normally closed kill swith & you can get .5-.7 for an entire circuit. Not so good, but that's what I've tested on a few bikes that worked fine. So battery volts may be 12.4 with key on, but volts to coils/EI may be less.

Testing short to ground with ohm meter works well though so long as consumers are isolated from circuit.

Battery charger amp rating doesn't matter to the Zener diode. It's the volts that starts making zener shut current to ground. So you have low battery. Hook up charger. Volts are now 13.2. All is fine. As battery charges volts increase to say, 14.7 or more. Now Zener will shunt current to ground. You will feel Zener getting warm to very hot depending on volts & now... the amps of charger come into play more amps of charger makes more heat. No cooling air flowing by heat sink, Zener can/will be damaged.

Fun to test this. Hook up volt meter. Monitor volts & put finger on Zener.

Zeners are fun to test in real life on bike, which is part of full charging system test. It really does show amps through Zener when volts are too high exactly like shop manual says.

You say the red wire to Zener, I'm thinking the earth wire to bracket?? As I recall that's on front fork. I don't know how much earth the steering bearings pass, but a short to earth inside headlamp shell might?? go to earth via the red wires to Zener. Just a thought. I've seen many melted harness. Often they will have greater melting at the point of the short working back to power source with Neg ground. Positive ground might be opposite. That I don't know.
Don.


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Re: Melted positive ground wire T100C [Re: TR7RVMan] #798196 02/12/20 8:04 pm
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on a side/side note ,
the ground side harness wires dont technically need insulation . ( the red wires )
the ground side wires are just an extention of the battery pole they are connected too .
they are as "hot" all the time , just like the battery pole ( meaning there are no switches on this polarity...but perhaps one fuse )

that the wire shows history of excessive joule heating is an indication of current flow above the insulation temperature limits
and probably voltage loss through resistance .

a large gauge wire or a paralleled wire could solve the problem ... or a ground wire closer to where the real loads still are .
( if the zener ground is up front like tr7man suggested ... the wire could be handling all up front loads and not just the zener .
if the zener is gone ... the connections from copper to frame are the Suspects ... especially if the insulation damage
Yes Ltd to the area close to a connection .

Re: Melted positive ground wire T100C [Re: vintage rider] #798208 02/12/20 9:31 pm
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When I wired my Triumph, I used some pretty heavy gauge stuff. 25 amp fuses are no problem on this bike. I blow them rather too often when working on the bike. I know, the first thing the instructions say is to disconnect the battery. Easy for you guys. Us pre unit guys have to dig out a 50p coin, unscrew the tool box cover (seems like 100 turns) to get to the fuse.
Never melted a wire yet.
I use the bladed type. They're everywhere now, even at the hardware store while the glass fuses are slowly dying out.
Put one fuse on the positive side of the battery and carry extras. I also carry a piece of stout wire to short the contacts if necessary. Not ideal. I know, but I'm getting home one way or the other, but not in the back of a pickup truck.

Cheers,
Bill


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1974 Commando
1985 Honda Nighthawk 650
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Re: Melted positive ground wire T100C [Re: vintage rider] #798211 02/12/20 10:39 pm
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As I understand, the power lead (Br/Bl) to the Zener is removed and isolated, so the the Zener is a redundant, decorative item.
The paired red wire connection is still connected to the Zener bracket/heat sink.
This merely provides 2 routes back into the red wire system, to the rectifier +ve and the battery +ve (it is important that those 3 points are reliably connected in a Zener system).
This lengthy link is now unnecessary. It would be far better to join the Tymp +ve directly to the SPG, and a lead from there with a fuse in it to the battery +ve. Then remove all that redundant red wire.
The SPG to battery +ve lead should be rated for maximum system amps, perhaps 2sqmm.

As has been covered, the original cause of the melting of that particular wire was most likely due to the Zener failure. That it melted the Zener ground wire without blowing the 20A continuous (40A blow) fuse suggests that the Zener failed in such a way that it passed a current around 20+A through a wire that may be rated for lower current.

The red wire system in these bikes typically includes a few connections to the metalwork of the motorcycle (ground I'd call it, sorry Stuart).
Some are a historical legacy from the times before proper red wire grounding systems, a few are essential.
The early systems connected grounds to nearby metalwork, sometimes a headlamp shell, a rear mudguard, or whatever. The battery +ve often bolted to an engine plate.
This worked well enough for a while, until corrosion stepped in, or maybe just regreased the head bearings.

Losing so much connectivity just isn't acceptable nowadays, when we need decent lights and maybe EI as well. The electricity must be allowed to flow as freely as possible. Hence the red highways.
It must not be forgotten that a connection to ground (best on the engine or engine plate) is important for the contact breakers and spark plugs to function.
A good connection of the engine to the frame to the red wire system should not be assumed, especially if the frame has been repainted.


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