Overheating wiring harness

[Midniteoyl]

Hi Gents. Thanks for your replies. No sharp edges for the wiring to chaf on. On further inspection, the loom has melted in at least four places and rather interestingly, the positive lead connected to the ammeter is also slightly burned. The flames appear to have come from some burning leaked diesel fuel which had run back along the tachometer cable! Hence why the fire died so quickly.
I have a dynamo rather than an alternator, but take the point about the voltage regulator. The engineer who restored the tractor has stripped out the burnt harness and we have compared it with the original 'tired' one which we took out. The wiring on the original does seem a bit more substantial.
As a result I have investigated buying an exact (as is possible) copy of the original lucas harness as I understand this is more substantial than the various replacements available. Once installed, we will be checking all cable and instruments etc. for shorts.

Is your tractor 6v? Wonder if the 'new' harness was meant for 12v conversions? 6v wiring is bigger due to higher amps..

 

[Coyote machine]

Also, if you're going to build your own harness and fuseblock I'd be inclined to step up to marine grade wiring. It has to withstand a harsh environment and is usually tinned copper. Ideally all connections are made with heat activated shrink wrapped connectors, which contain an anti-corrosion gel. It's not that much more in terms of expense, and is well worth it in peace of mind, and once and done results.
Yes to replacing VReg, and as suggested, make sure the wiring is rated to the voltage of the machine.
You should be able to find some marine wire sellers in your neck of the woods; after all you're on an island, no?:thumbsup:

 

[Looking4new]

These guys are in the U.S., but they sell wiring harnesses.
Painless Performance

I have no connection with them and will see no rewards for recommending them.

 

[DAG1]

Gents

Thanks again for all your help and comments. Decided to fit a Sparex harness as it was obvious it is of better quality than the Agriline one and therefore as good as using our own wiring. Included a fuse and tested for any shorts etc. Interestingly, as we were about to close the bonnet (hood!) we noticed a very small black mark on the underside above where it covered the negative terminal on the battery. You've guessed it, the black mark was evidence of very slight burning so it would appear the harness shorted out via the terminal touching the bonnet! Feeling like a bit of a plonker (idiot!). Have now covered the battery with rubber insulation and hopefully will have no further problems, fingers crossed.

 

[BleedingOrange]

After reading your last post, I,m confused. Isn, the negative post ground ? If it is, then touching the bonnet shouldn,t of been a problem. Not that it never should be touching it. Does the positive post have any black burn marks above it ?
Normally, that,s the one that should be protected from touching the bonnet.

 

[Coyote machine]

I agree that the negative terminal should not cause a dead short, which is what you were referring to about the arcing to the hood. BUT, it's possible that there was enough transient/static energy at the area that the charge jumped the gap and passed from the negative side to a bigger/better ground, the hood and in the process passed the unregulated current through the harness. Whatever happened, the battery needs to be completely isolated from any metal. Be careful the posts don't wear through the rubber; personally I'd find a different way to make sure the two can't connect under any circumstances.

 

[Midniteoyl]

Is this a POSITIVE ground system?

 

[DAG1]

Gents
Feeling a bit silly! Desperate to find out the cause of the fault and on seeing the burn mark under the hood, jumped to the wrong conclusion. As Guido455 says, it would be the positive post which would show burn marks. Would love to think Coyote machine is right as can find no other cause of the problem. Will keep an eye on the ammeter and carrying a fire extinguisher! Any other thoughts will be very welcome.

 

[Coyote machine]

I'd want to find a way to make the battery fit without a possibility of a post grounding on the hood, without the rubber cover over it, if at all possible. Peace of mind and no other damage likely.

 

[Daver1963]

Fuses fuses fuses. A properly constructed wire harness includes fuses to stop this sort of thing from happening. enough current to melt it in 4 places, should have popped the fuse! Even the wire to the starter should have a fusable link. It may be wise to hand construct a harness with larger wires, fuses and use a spiral plastic wire loom to protect the wires from chaffing shorts. These old machines have little electrical so the wire harnesses are simple enough to by hand one wire at a time.

Good luck and maybe you should think about mounting that fire extinguisher on the tractor?

If you do go to the "hand construct" method for your harness and can't get big enough wire loom or if the wires just go in too many directions to make the wire loom practical you may want to consider some cable lacing cord. The product that I linked is wax coated which makes it somewhat sticky to itself and will hold in place as you wrap it around the wire harness.
There are different methods of cable lacing. This page shows a few: Cable lacing - Wikipedia, the free encyclopedia