Help! Toasted CDI and melted wire!

[Wyldesoul]

Right. I did a search and couldn't find much info.


I've got a couple spare CDI's, so the replacement of the CDI isn't an issue. What I need to do is make sure that this doesn't happen again.

1981 GS750

I'm in the process of fixing it up to ride, and have just replaced the Regulator/rectifier.

I replaced the RR, and hooked up the bike to fire it up. I turn on the key, and go to hit the starter. It cranks, but then I notice smoke. A lot of smoke coming from under the seat. I am able to get the seat off and I notice that the CDI is smoking. Grand.

After the smoke stops, I found that a wire had melted right next to the CDI, and had burnt off all of its insulation all the way into the main harness bundle.

I'm able to find some unburnt insulation, and discover that that is the black with white stripe wire. The main ground wire.


Wiring diagram shows that from the CDI, it just goes straight to chassis ground, after coming out the back of switches and bulbs.

Now, the R/R I just installed is the Shindengen SH232. I wired that up according to a write up that I saw before.
3 yellows to the 3 stator wires
Red to battery
Black to hot while running (Orange/green wire supplying power to brake light switch)
Green to chassis ground.

I was definitely confused at that, as I had thought that black was universally the ground color, but that is what the writeup said to do.

This does, however, raise my suspicion that green is NOT ground, and that I was shorting to ground through the R/R.


Please help me! I don't want to have my spare CDI burst into smoke like this one just did, but I am SO CLOSE to riding this bike, and am itching to get back in the saddle.

[Flyboy]

Mmmmm?? Sounds like you have it right, green is ground alright, here is Duane's PDF with the mod details.
You maybe want to go through the harness with a fine tooth comb and check for chaffing somewhere, also sounds as if your main earth is dodgy, when you hit the starter you are pullng lots of amps and if the main earth cable is not up to snuff, the system will try and earth wherever it can, which is your little black and white wire/s, and off course that is nowhere near enough to handle the amps while cranking, so it over heats and burns up.

[tom203]

The green wire needs to be chassis ground , but also have good direct connection to battery negative. Does your ignitor have a ground ring that was connected in the area of the old stock R/R? if so, connect this to same place.

[Wyldesoul]

Well, what I'm doing now is I lengthened the green wire so that it can reach battery negative, I put a bullet connector on the red wire so it can hook up to a fused positive rather than straight to battery, and I put an inline 10A fuse into the ground coming from the CDI. I'm going to put the new CDI in and check it out after the rewire of the R/R. If the issue occurs again, I'll just go through fuses rather than CDI's.


Wish me luck on this working.

[Nessism]

Your bike doesn't have a "CDI", it has an transistorized ignition that uses magnetic "signal generators", and an "igniter", which fires the coils.

[Wyldesoul]

Right. Thank you for your wonderful pearl of wisdom in assisting me towards preventing my igniter from burning up.

[Flyboy]

Uncalled for.

[Nessism]

Right. Thank you for your wonderful pearl of wisdom in assisting me towards preventing my igniter from burning up.

Sorry man, couldn't help myself. Your seven references to "CDI" made me jump.

Black/white is ground as you know. You have a dead short between that wire and the battery somewhere. I don't understand where you tapped into the wiring with your R/R installation, nor do we know for sure if that is the problem anyway. What we do know is you have a short, and that sort of thing is hard to diagnose on the internet.

Good luck and please don't burn up any more of those CDI's...er, igniters.

EDIT: just thought of this... when you bypassed the factory harness to go straight into the R/R, what did you do with the old harness terminals. Could one of them be shorting against the frame?

[Wyldesoul]

Sorry I got testy.. Just... yes.

The wires I bypassed were taped off to seal them from the frame.

So.. You have the 1 harness that goes to the signal generator.

The 2nd plug, 1 wire goes to ground (burned)
2 wires go the the coils
And the only wire that receives power is already hot in run.

So... Is this just a sign that my CDI (Just to annoy) is bad?


The only way I can possibly figure that I would have a short to power that burned the ground wire from the igniter box (and I mean RIGHT OUT of the igniter box), is that there was an internal short in the box.

There is nothing else that makes sense. But how would it not burn the orange/yellow 12v hot (while running) wire that is the same gauge as the wire that was burned up (With enough heat to vaporize the insulating wrap around the bundle. And melt the wire right next to the igniter.

What if the battery box (which is metal and which the igniter is bolted to, and which is isolated from frame) somehow got 12v hot? Gah. That is the only thing that I can think of that would at all explain what happened....

Ah well. At least I'll be able to test it now while only blowing fuses, rather than CDI's. :P

[Flyboy]

Nah, it's all good, these wiring issues can drive a grown man to drink at the best of times, I know that I am pretty dim with that.
But the senior guys here like Nessim and a bunch of others know these bikes inside out.
Sorry I could not be of more help.
I am off to wear my fingers to the bone polishing fork stanchions