burnt ground wire

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Jul 24, 2007
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still trying to get this damn bike to start. in the process of cranking (short bursts) the engine over with the electric start i started to get smoke by the aluminum capacitor mounted in the spring. checked it out and there is a red wire which runs from the battery to the headsteady. it obviously has gotten a little hot and managed to melt the insulation on the wire. the ring terminal was underneath the top nut of the headsteady (this is the original headsteady.) Possibly a poor grounding location because of the rubber?

I have a proper 6awg wire from the + battery to the engine. Is this burnt red wire a ground for the points? I wouldn't think so but i seem to be missing it's relevance. Also would this wire give me issues with starting? I have a nice blue spark on both plugs and have properly adjusted my timing. Thanks ~Gavin
Ground wires are as important as power wires. If you have burned one, high amp power that is trying to return to the battery is not finding the pathway intended. A strong battery is capable of melting down the whole works How do you think those French guys invented arch welding? Check that the intended pathway is in fact good I don't think it is.
i understand i'm for some reason drawing too many amps through that wire, but i need to understand why it's there so i can figure out why i burnt it. And if it's in the wrong location. my dad pulled the heads a few years ago and never ran it.
Thats kind of the whole point. A ground wire burnt. The high amps were on their way back to the battery not drawing down power , failing to return power. I don't mean to be a hard case on ya you just need to think this through. First if you still have good spark lay off the start button and kick the bike over. If it doesn't start with three kicks somethings wrong. Fuel, spark , air. It's possible that the starter is drawing down the battery to the point that the coils can't make a spark under the load of compression. Lots of spark with plugs out no meaningful ones inside. By the way are the plugs new and gaped for points?
plugs are new BP7ES and i haven't gapped anything. spec is .035 right?

i've been trying for like 3 days to get this thing to start. i was just using the old dry fuel lines propped up to start it since i was sealing the tank. finished the tank yesterday and put a good gallon on fuel in it thinking i wasn't getting enough volume or pressure. i soaked and rebuilt the carbs new throttle needle and needle jet pilot jet is clean. i've set the timing and im not running a filter initially. all i get is an occasional black puff out the mufflers. i've got even exhaust pulses also so i can rule out a stuck valve. ive got a new strong battery also.
GavinJuice said:
checked it out and there is a red wire which runs from the battery to the headsteady.

You should disconnect any red harness wire from the battery. ONLY the heavy ground wire should be connected to the positive (Earth/Ground) side of the battery.

Whoever designed the wiring harness got this WRONG. And they got it wrong on the electric start T160 Triumph Trident too.

If for any reason the heavy positive starter wire is not making proper contact, either at the battery or at the crankcase connection, when the starter motor is operated the heavy starter current (100+Amps) will try to take an alternative path back to the battery through the red harness wire = NOT GOOD.

Triumph issued a service release to dealers recommending the red harness wire battery ring terminal should be disconnected, cut off and the end taped back to the harness.
I don't know if Norton ever issued a service release concerning this problem, nevertheless the same thing should be done to any electric start Commando model in my opinion.

Just make sure you have a good ground wire between the cylinder head and the red harness wire.
Just expanding further on LAB's comments.. and after many years in the auto electrical field~

Essentially current passes from the battery thru (in this case ) the starter motor and back to the battery !

There fore to gain efficient performance the cables have to be adequate. As Les says in application of a starter motor ~ 100 amp ~ If not slightly more ~
In fact the earth cable should be the same size as the positive cables to the starter and or solenoid

But the earth cable should run from the negative side of the battery ~ ideally to the body of the starter motor . not just from the battery to the frame ~ as every joint represents some degree of resistance!

If the "Earthing" or "live" cable/s are inadequate when the starter is cranked over the power cable OR returning current will take any and the easiest path from and back to the battery ~ and if the only path is inadequate the thing will simply MELT ~

(I believe that this was typical of the faults in the original Commando starter ~ inadequate cabling and contacts ~ along with too small contacts in the original solenoids~ )
Can we get something straight here, Gavin, is your bike wired consistently as either negative ground or positive ground?

If you have red wires running to the chassis, head steady, et al, then your bike is (should be) positive ground.

If for one moment you forget this scheme and wire up just one wire as a negative ground scheme you will have a short which will cook a wire somewhere.

Forget spark or carbs, you seem to have a wiring problem first and foremost.

My Eu.02 :lol:

Good luck and cheers,

NoHoNorton has made a excellent point/s ~
The earth configuration is important ~ neg or positve earth ~ I assume you have positive earth, as original ..

But my main point is that regardless.~ the cables ~ earth and power particularly in the starter circuit shoud be the same; 'heavy' gauge ~

Think of an electrical circuit as you would a garden hose..

Why would you have half the hose 1/2" and the second half 1/4" ~
Same deal ~

And yes ~ totally agreed ~ forget fuel , points , ignition ~ essentially work on cables.
Just to clarify everything is still a POSITIVE earth system. Ive replaced the 3 main cables with all 6awg wire so there's no issues there. To begin with ive got a total of 3 wires going to the Positive terminal. The thick 6awg going to the crankcase, one red wire which WAS going to the headsteady, and a third which follows the harness back. I'm not sure where it goes without tearing out more electrical tape. If what LAB says is right, then i will disconnect and see where it ends. LAB's comment makes sense since none of the wiring diagrams ive seen show more than just that crankcase ground off the battery, that has has me confused for some time.

The whole reason for starting this post was to figure out why i was melting that obsolete red wire. I think norbsa and i weren't fully understanding each other.

BUT honestly i don't think melting that red wire has anything to do with my starting issue. it's just a coincidence it was happening at the same time.
The head steady bolt into the head was used to earth the engine. By the way if you have points a .035 gap is too much .025 more like it.
The heavy earth on my Mk3 runs from the battery to the rear engine plates and bolts on near to, if not to the inner primary center mount.

I don't think it was a coincidence that that head earth melted, however, be carefull as it may well have melted the insulation on other wires wrapped in the harness
when i pulled all the electrical tape off, there were about 3 red wires all coming together at a central point which were crimped and soldered together. It's already soldered there so I'm going to snip and tape off the end of the cable and be done with it. Now i just need to find out where that other red wire goes. Oh and set my gaps. Thanks alot guys ~Gavin
There should be a red wire with a ring terminal that connects to the rear frame in the area of the starter solenoid, or even connected to one of the solenoid mounting bolts?.
Could it have been connected to the battery by mistake?
Or is there a red wire terminal connected to the frame near the solenoid already?
yep that red wire is there. i removed the solenoid to replace those wires and i made sure to put that red wire under the nut. Man those are a bugger! I was only able to get one closest to the outside on, the other i've left off. I also ohm'd out that third red wire from the battery, (which ran back in the harness) to the red wires on the coil and the red wire under the solenoid. What i should do it is see if there is voltage at those points with it disconnected from the battery. But i don't forsee that happening since there is literally no room in there once the battery is in place. So it's gonna run for the time being. ~Gavin
I am still curious why that wire got hot and smoked.

Snipping it may SEEM to have cured the problem but I suggest using an ammeter inits place and see what kind of current is flowing. I predict a lot.

The next question is why is all this current charging along this route?

One has an engine with a starter motor that is electrically isolated due to the rubber in the isolastics so it relies on a ground wire from the head steady.

My guess is that the starter motor and/or solenoid has a reverse connection, the motor assembly is negative ground in relation to the rest of the bike.

Easy enough to check with a voltmeter. With ignition turned on, battery positive to head steady should read zero volts. If not then there is a wiring problem.

NoHoNorton said:
I am still curious why that wire got hot and smoked.

Snipping it may SEEM to have cured the problem but I suggest using an ammeter inits place and see what kind of current is flowing. I predict a lot.

The next question is why is all this current charging along this route?

I believe I have already given the reason here why this occurs.

= If the heavy gauge positive ground battery wire is not making proper electrical contact either at the engine or battery because something has loosened, corroded or is not fitted correctly, the starter current re-routes through any harness ground wire that happens to be connected to the battery ground (in this case = positive) terminal when the starter is operated.


As this smoking red wire problem only occurs when the heavy pos. starter wire is *not* making good electrical contact I suggest you re-check or reposition the heavy wire terminals, as it is apparently not making proper electrical contact somewhere?
thats what i would assume, a bad connection at the crankcase. But there is NO reason that red wire should have run back to the battery. It was serving no purpose. I'm gonna check the voltage drop on that new cable from the battery to the crankcase. That would show if i am having an intermittent connection. Hence that burnt red wire. I ohmed out all the wires when i replaced them and they were all less than an ohm.
Hopefully you will at least have cured the ground wire problem.

But of course there is still the non-starting problem.

And if you are getting reliable sparks (check by turning the engine over with the plugs out and resting against the cylinder head), and there is adequate fuel reaching the cylinders with good compression, then theoretically it should start, or at least show some signs of it, provided the sparks are occurring at roughly the correct crankshaft position.

Are you 100% sure that you have set the ignition timing correctly?
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