Electrical fire

[thepom]

So I,ve just rebuilt the xt 600 after the fifth gear problem and followed the book......filled it with oil and started to crank it over by the electric motor and smoke everywhere... found a black wire coming from the loom to the negative side of the battery had completely melted the plastic coating.,
What have I done to cause such a short circuit? have I done something wrong when fitting the alternator? answers on a postcard to ......any help more than welcome

[bogan]

So I,ve just rebuilt the xt 600 after the fifth gear problem and followed the book......filled it with oil and started to crank it over by the electric motor and smoke everywhere... found a black wire coming from the loom to the negative side of the battery had completely melted the plastic coating.,
What have I done to cause such a short circuit? have I done something wrong when fitting the alternator? answers on a postcard to ......any help more than welcome

yup, if the alternator is the only bit of electrics you have touched then thats very likely to be the problem. Though was the smoke caused when you cranked it over? or when you turned it on?

[thepom]

It would not crank over from the starter motor so I checked the fuse and moved some wires then it just cranked over for a second then started smoking....I had the ignition on but no problems...only started smoking when it turned over for a second...

[bogan]

It would not crank over from the starter motor so I checked the fuse and moved some wires then it just cranked over for a second then started smoking....I had the ignition on but no problems...only started smoking when it turned over for a second...

when you say moved some wires, like pushed them around, or plugged them in different places?

[thepom]

just moved them around,little shake here,shake there.....

[bogan]

just moved them around,little shake here,shake there.....

hmmmm, I would recomend tracing the faulty wire back to where it shorted and fixing that then, may need to take apart the loom a bit though

[thepom]

just checked the wiring diagram and the only black wire goung back to the earth comes from the reg/rec ...which has 3 white wires coming from the alternator....

[Ixion]

It's probably not a short circuit, just you have missed a wire. Is the black wire from the loom quite skinny? There should be a skinny black wire , and a honking big fat wire (cable really) going to the negative terminal. Fta cable doesn't come out of loom, it's a separate cable.

Skinny wire handles earth for bike electrics, fat cable handles high current for starter and alternator (earths the engine unit). Hunt around for a fat cable, trying to put starter motor current down the skinny wire will def burn it out.

[thepom]

yeah it was the skinny black wire that melted the plastic.....it is joined together with a bullet connector...never thought it should have a bullet connector there and it was covered in electrical tape.So you think I might have missed a connector somewhere?

[thepom]

just pulled the starter motor and slaved in to the battery and that works fine,looked round for more cables but the fat neg goes to what looks like the starter relay and then to the starter,will look at the reg rec next which is under the tail cowl but have to go to work now so it will be tomorrow,thanks for the help so far,all I,m worried about is there anything I removed like the side casing which can cause it to short out from fitting it wrong?I did remove the rotor to split the casings but never removed the stator assembly....

[Ixion]

Fat *negative* goes to starter motor ? ie that implies positive earth ?

[bogan]

so you got fat wires coming from both battery terminals right? one goes to starter relay then starter, other goes to a frame/engine ground.

[Ixion]

Yes. Should be a fat cable and a skinny wire on each battery terminal. Positive one usually red , usually goes to starter. Negative one usually black, usually goes to earth (maybe not directly) . Def want a thick and a thin on each terminal. Don't put starter current through a bullet connector !

[Motu]

Don't assume that a black wire on a Japanese bike is earth - they don't use logical colour codes like Lucas.The starter wire will come from the solenoid,the other side of that will go to the battery....it's a pretty direct link and should be obvious.The negative wire from the battery will just bolt to the frame somewhere.

[CookMySock]

You have left the heavy negative lead off. It goes from the battery to the frame.

Steve

[scumdog]

It would not crank over from the starter motor so I checked the fuse and moved some wires then it just cranked over for a second then started smoking....I had the ignition on but no problems...only started smoking when it turned over for a second...

Wow, lucky you stopped cranking when you did 'cos if ALL the smoke had escaped your starter wouldn't work any more.:shit:

Listen (read?) to what Ixion etc are telling you.:yes:

[Pixie]

If it had Lucas (Prince of Darkness) Electrics you can buy replacement smoke for it:

http://www3.telus.net/bc_triumph_registry/smoke.htm

[thepom]

Ha ha what a wanker I turned out to be....just found the other end of the negative earth cable floating around not connected to anything ,now all I have to do is find out where its bolted to and replace the burnt wire and try again.......now where was it bolted to????

[CookMySock]

Normally it's held by one of the engine cover bolts. Just sorta let it flop where it wants, and it will tell you where it goes.

Steve

[thepom]

yeah spot on,goes to one of the two starter motor retaining bolts,going to replace the wire now and try again...

[CookMySock]

I was told there is a very good reason for that little black wire that got fried, but stuffed if I can see why it's necessary.

Steve

[notme]

I was told there is a very good reason for that little black wire that got fried, but stuffed if I can see why it's necessary.

Steve

Think 4 wire measurements type scenario - from reading your other posts you're prbably well aware of what that is. The skinny earth is for the solenoid or some other low current circuit, if the power earth was used, the current down it would cause it to be some voltage drop above earth and thus a bad "earth" for the solenoid or whatever. Imagine if the fat wire was the common earth for the solenoid and the starter current - the solenoid clicks in, the starter pulls a big current down the earth wire, the solenoid now has a connection to +12v and something a few volts above ground, so it drops out........rinse and repeat, and woder why your bike doesn't start!

On my very first car (Austin 1300.....don't even ask!) I once left the starter earth off after replacing the Bendix gear type starter. The starter found an earth path just fine and started her up, but for some reason the acelerator pedal wouldn't move. The accelerator cable welded itself to the firewall......

[CookMySock]

Yeah that makes sense - keeps the electrical system fully-powered while drawing large currents to the starter.

Steve