Melted wires short circuit

Hi there!

So I installed a custom sissy bar / luggage rack on my XJ750X today only to crush my tail light's wiring and causing an unintended electrical smoke show. I re-installed my rear fender without concern for the wiring underneath traveling to the tail light, and upon my trial run with my proud new rack, my bike began to smoke like crazy and shut off. I immediately turned the bike off, removed the seat, and got the "privilege" of seeing my ground wire on my main harness bubble and melt before my very eyes; a very sad sight.

So I traced the problem back to the crushed wiring under my rear fender. I am not an electrician so here are my questions:

1) Can crushed wires, even if the outer insulating material and wiring jacket are both still in tact, cause a short circuit? (the three wires traveling to the tail light are literally completely flat yet unexposed).

2) I need to replace the burned out wire(s). Fuses are all okay. What other side effects are known to happen to 80's Yamaha's after short circuiting the ground wire on the main wiring harness?

These are very specific questions. I hope some of the great minds on this forum can offer some insight into my dilemma.

Thanks everyone!

Jerry
1985 Maxim XJ750X

 

1 - well all the wires on my bike are the kind where many strands of copper twist round eachother and and encased in a plastic sheath.
Each of these only carries one signal/current/whatever.
crush it, deform it, as long as the inner strands don't break and as long as the plastic sheath doesn't split then its fine.

If I'm working with something like a micophone cable, there are usually two inner wires and a braided metal sheath all wrapped up in an outer rubber sheath.
crushng a mic cable may result in the inner wires touching eachother, but none of your cables are like that right?

do a quick test on those wires with a multimeter.
1st, check that they still conduct current (all the insides are ok)
2nd, see if they are conducting through a split you cant see.

as for your question 2, I imagine the things to get nervous about would be the TCI and the reg/rec.

 

Jerry,

Run a known good taillight wiring harness in place of the melted one. It should be easily obtainable. But, before you attach your "New" taillight harness, check the main harness where the three wires plug in and verify each circuit is good.

The black wire is the ground. Check for continuity to ground and make sure there's no power feeding into that one (with the key on or off).

The blue one is for the running light. It will only have power with the key on. Verify it's not shorted to ground.

The yellow wire is for the brake light. Make sure it's not shorted to ground and it will only have power to it when the front brake lever or rear brake is applied.

You will need to disconnect and repair any other wiring that has melted on the main harness. A wire with the protective casing compromised will still flow electricity, however you will want new sections that minimize the chance it doesn't short out again.

Tony

 

If the wires are crushed there will be an electrical hotspot there and it will be kind of like a resistor in the sense that current will not flow through it like it should.
If the wires are crushed enough the spot will get real hot.
Change the entire run of wire to do it right or just cut out the bad spot and put in a new piece as a band-aid.
As for other side effects, if the fuses are still good then I don't think any real bad stuff happened to the rest of your electrical system.

 

That's a worry....why didn't your fuse blow?

 

So my crushed wires are actually a distraction from the real issue.

Upon further inspection, my negative ground has a jumper wire connected to the ground on my main harness that someone previously installed to bypass the main fuse. :-(
What seemingly happened is the jumper cable had some damage on the covering and when i placed my main seat, the wire must have made contact with the positive terminal and fried the line.

So, I will proceed by replacing the burnt wires, checking voltages and ohms on the most immediate electrical components, replace tail light harness, and figure out why the main fuse has been bypassed.

Any other suggestions, comments, ideas?

 

that made my head hurt!
there are no fuses on any ground wire anywhere on your bike. that means nobody can bypass a fuse with a ground wire.
if a ground wire going to the tail light burned, there has to be a positive wire burnt too.
if your saying the added-on ground wire touched the fuse block, thats a good reason to put a new fuse block in, one with a cover on it.
if the wires going to the tail light are just pinched, you can just cut them at the pinch and solder and shrink tube them. then test the harness right to the bulb connections

 

Polock. You are correct.

I have thoroughly investigated the burnt wire and it appears that the issueis my one grounding cable that piggybacks off my negative ground near the battery terminal. That cable connects with 2 other grounds, forming one bigger cable which i believe is 12 guage, then continues to travel up close to the front of my frame where it splits again into 2 18 guage cables and 1 12 guage cable that grounds off to my frame.

So far, I have found no other damage and will finish the job tomorrow once i get the right connectors. Hopefully the rain stays away for another day.