Topic: Smoking Wiring Harness $#@!

[Dunstall_74]

I worked on my cb750 all day yesterday and just as I was nearing the end of my day, I decided to put my newly charged, fresh high performance battery in.  I did not realize, that this new battery had the poles in the opposite positions as my old battery, so the first thing I did was hook up th leads, just as they were with the old battery, because they are naturally set up (length wise) to fit that way.  Bad Move!  I shouldn't have assumed that this new battery, even though it looked basically the same, was set up the same. 

Now for the Smoke.....  I hooked up the negative lead on my bike to the positive pole on the battery.  I was in the process of trying to bolt on the positive lead,(to the neg pole on batt.) and then the smoke started rolling off my wiring harness.  The smoke was coming from the harness plug that is located right next to the grounding bar where all your grounds are connected.  I really know very little about electrics. I freaked, and immediately unplugged the terminal plug that had smoke rolling out.  It was then that I realized the mistake I had made.  I unhooked the battery cables, switched them to the proper positions, checked the fuses and now nothing works.

Has anybody ever encounterded this?  I have checked the fuses and they seem to be intact.  Where is a good place to start?  Is there more fuses than the main, headlight, taillight,  that I'm not aware of?

[Patrick]

Go back to the area where you saw the smoke and look for a wire with melted insulation that allows a short to the frame.

Patrick

[Gordon]

You're not alone on this one.  I did the same thing with my 550 a couple of years ago.  Most likely you fried the rectifier, as it only takes a very quick reverse polarity to kill it.  You also probably melted the insulation off of the green wire that comes out of the rectifier, and possibly some of the surrounding wires causing a short which could explain the complete lack of power.

[GammaFlat]

I'd go along with the "rectifier" theory.  I've done the same (in a different application) and replacing the rectifier straightened out the problem. 

[754]

I HATE the smell of burning Kapton isulation in the morning 





afernoon, evening and night too .. specially after midnight on the road..

[TwoTired]

Reversing the polarity on the rectifier, with nearly unlimited amps, is nearly guaranteed to kill it.  What worse is even if you now put the battery in with correct polarity, more wiring will burn due to the high likelihood that the rectifier is now shorted.

The charging circuit is NOT fused, so do not expect fuses to save anything with such a mistake.

Check the wiring in the harness between the rectifier and the battery, as well as all the connectors in the path.  If these wires are in a bundle, you have to check the insulation on neighbor wires.  Hot wires melt their insulation, too.

It's a tough lesson. But, now you know the importance of + and - .  It's not likely you'll make that mistake again.

Cheers,

[Gordon]

It's a tough lesson. But, now you know the importance of + and - .  It's not likely you'll make that mistake again.

Ain't that the truth!  I now check the polarity about four or five times before connecting any battery.  I'd rather not deal with that mess again. 

[Steve F]

Uh-oh, you let the smoke out?  The price of replacement smoke these days just keeps going up, and up.  Bummer to hear about the harness, rectifier and all the other unseen parts.  Chin up, It'll work out since I've seen worse than that get fixed up.

[Tower]

I asked my son for a boost last year.  He crossed the wires.  Burned and melted wires and insulation was the result.  Couple of wires were fused together and no electricals on the bike would work.

Had to follow the burned wires until they weren't pickled, cut out and replace sections in the main harness, add new connectors, insulation and wrap.  But, those hardy electricals were all OK!  You might get lucky (relatively speaking) as well.

[narcoticrex]

I did the same thing but luckily didnt fry my rectifier, nor anything else. Whew that was a close one.

TwoTired said that the charging circuit isnt fused...wtf Honda?  The rectifier is the one thing that will met down and its not fused??

[HondaMan]

I did the same thing but luckily didnt fry my rectifier, nor anything else. Whew that was a close one.

TwoTired said that the charging circuit isnt fused...wtf Honda?  The rectifier is the one thing that will met down and its not fused??

Well, barring this kind of mistake,...the alternator can only generate 14 amps when shorted to ground. That's not even enough to heat up the wires. Japanese (and American!) cars don't hold up well to this special test, either. 

[TwoTired]

TwoTired said that the charging circuit isnt fused...wtf Honda?  The rectifier is the one thing that will met down and its not fused??

Well, to further this line of thinking, the rectifier isn't armored to protect from hatchet attacks, or shielded from explosive charges and ballistic projectiles either.  Was not adding cost, to protect for this, short-sighted by Honda, too?

Adding devices such as fuses and fuse holders introduces in-line resistance and extra points of failure, in a fairly simple system.  Honda designed the bike to be serviced by qualified repair personnel, not to withstand abuse by anyone who isn't thinking clearly or with intent to destroy.

As Hondaman said, the rectifier needs to hold up under the charging currents from the alternator (which it does, handily).  Not the hundreds or thousands of amps that are available from a charged battery under direct short conditions (as in when the diodes are forward biased due to polarity errors.)

Cheers,

[fastbroshi]

Did yours look something like this?  Same situation here...

[HondaMan]

Hey, RXman: look familiar? Isn't that the same wire you taped up in the Safeway parking lot last year?

[Dunstall_74]

I think I may have gotten lucky.  Not sure how to check if the rectifier is ok or not, But I've got juice.  When I hooked up my ground lead for the battery in the new spot, to reach the -batt. terminal, It was not a good enough ground as it had a rubber washer.  I hooked up a new ground point on the frame and problem solved.  For now anyway.  I looked the wires over in the area where the smoke was coming from, and everything appeared to be ok.  There was a terminal coming off the starter solenoid that had melted the terminal insulation a bit.  It had actually come unseated from the terminal because of it, I had to trace that one down because after I found a good ground I lost power again briefly before finding this item.

I have since taken the bike for a cruise, just for a few miles.  It ran great.  Hopefully I don't have any underlying problems, i.e. rectifier, melted wires. Don't need anymore electrical problems.  Electrical has got to be my least favorite part about working on this bike.

[Gordon]

I think I may have gotten lucky.

I hope so, but chances are the rectifier is still toast.  The bike will run fine without a working rectifier, it just won't charge anymore. 

[fastbroshi]

  My pic above isn't great and doesn't show it all, but darn near the whole length of jacketing on the ground wire was burned off on mine.  But it would still run fine!!  The only reason I found it was becuase I took off the tank and other miscellaneous parts to get to the carbs.  I noticed the main connection for it near the coils was kinda funny lookin.
  After testing my diodes, none of them were allowing voltage both ways, but one was allowing over twice spec.  So it might not hurt just to give a peek down there.