Topic: New battery and wire harness causing elec smoke

[TimboTec]

So a little backround. Rebuilding a 750K6, new wire harness hooked up to just the basics (starter, battery, ground, Alt, rectifier ect...no lights) bought a 12v Agm battery for a battery shop yesterday came about 50% charged. hooked it all up and it got the starter to turn over.  Overnight I put the battery on the charger and got it fully charged. Today I went to hook everything back up and the smaller gauge wires leading to the rectifier and a few other places started to smoke and melt. I immediatley pulled power from the battery.
Question is, have I done any perminent damage to the wiring harness, no fuses were blown which surprised me.
I did have to get a new positive battery cable from the auto parts store, its 4 gauge which I know is much larger than the stock ones, would that have any impact on the issue?

Any electronics gurus help is appreciated

[Bankerdanny]

My best guess is you hooked something up backwards. Using a heavier gauge than necessary positive cable wouldn't cause that, reversing the polarities could.

[Yamahawk]

Yep, what Danny and Cal said lol.. if you let the smoke out, it doesn't work anymore.
Charlie

[TimboTec]

Ok, all great info. Thanks.

Just for giggles I went to an Car Audio supply store and got a 6 Gauge wire instead. Hooked it all back up and now NO smoke and starter kicks over. So weird right?! As near as I can tell it looks like it was just 1 green wire that fried (from wire harness to the rectifier), could that have been the short??  I tested the wire and it still has continuity so i wrapped it up with electrical tape. Would you drop the $$$ and get a new wire harness or keep on trucking?

[madmtnmotors]

Just replace the smoke:





 

[Yamahawk]

Lucas factory replacement smoke isn't compatible with Japanese bikes, as it comes out the right side instead of the left...
Charlie

[PeWe]

Lucas factory replacement smoke isn't compatible with Japanese bikes, as it comes out the right side instead of the left...
Charlie

Mexican smoke is very good what I heard in the 70’s. Using that before connecting the wires will guarantee more smoke.

In this case, check the circuit diagram.

[Bodi]

Except for the starter motor, nothing "normal" on the bike draws enough current to smoke a wire. The usual suspect is the rectifier, there are 6 diodes in there that can fail, and they WILL fail from even a momentary reverse battery connection. Diodes fail in one of two ways - "open" with no connection, or "short" which is pretty self explanatory. A shorted diode in the rectifier is about the only thing (other than connecting wires wrong) that can smoke wires, and they often do just that. There is no fuse in the rectifier circuit so the wires will melt real good.
Try with the rectifier unplugged. Measure the current from the battery with rectifier connected and disconnected: with key off it should be zero, with key on it should be well under 15A. Do not try electric start with a meter between battery and the harness + connection, that fries meters or blows their fuse if they have one. Most digital meters (except really cheap ones) have at least a 10A DC current scale.
Motor cable or battery to solenoid cable gauge won't matter, except when starting and even then only a too-small cable would be trouble if it overheated.
Check your ground connection from battery to frame, this is a starter motor power connection as well as the main system ground for most loads.

[TwoTired]

Did you paint your frame?
Did you scrape frame to bare metal all green wires that connect to frame?

When I acquired a bike with burnt/melted harness wires, I just replaced the wires in the harness that were burnt.  All other electrical components were good.  The damage was consistent with connecting the battery up backwards.  There are no fuses in the charging circuit, btw.

Cheers,

[TimboTec]

The frame was powder coated but i check the main frame grounding wire and the one under the seat and they all have continuity through the wire harness. Also, I left the battery hooked up last night and came out this morning to a dead battery.

Are these issues related?
The only things hooked up where the battery to the starter solenoid and power to the wire harness (black wire).

[dave500]

I think classic case of reversed polarity in connecting the battery?the harness main green earth wire will be melted maybe taking out wires next to it?

[TwoTired]

The frame was powder coated but i check the main frame grounding wire and the one under the seat and they all have continuity through the wire harness.

Continuity only means an electron pathway is available.  It does not imply any large current carrying ability.  Powder coating is an insulator.  You should visibly check the contact area is free of powder coat.

Also, I left the battery hooked up last night and came out this morning to a dead battery.

Are these issues related?
The only things hooked up where the battery to the starter solenoid and power to the wire harness (black wire).

Confusing.
The black wire is supposed to be switched power, only active when the key switch is turned on.  If you wired battery power direct to black wire, little wonder why the battery went flat. 

Cheers,