TOPIC:

Hi guys,

I'm hoping somebody might have an inkling of what is going on. Lately my 1978 KZ650B has been blowing the 20A main fuse when the ignition is turned on.

FACTS:

The fuse doesn't blow when the kill switch is in the off position. Headlight comes comes - everything looks good.

As soon as I flip the kill switch to run, the main headlight and the leds go dim and then boom - fuse blows.

I have a older Dyna III ignition.

I haven't done the relay mod.

After I replace the fuse, if I put it in first, pull in the clutch and roll it a few feet, I can start it without the fuse blowing.

Once the bike starts, she runs amazing.

My hypothesis is that when the Dyna ignition causes the coils to short, it is causing a short in the wiring. But why would it only happen at startup?

Any ideas would be MUCH appreciated.

You need to start checking every connection from the battery to the starter. You would be suprised how many connectors are corroded since that most of our bikes are 25 to 30 years old. I had the same problem on my 1000st/ Once I got inside the fuse box, I found that the wires inside were loose and arching into each other (By the way, I posted a fuse box replacement mod in the filebase). Sounds like something is shorted for sure. Since you have been in and out of the fuse box...it looks suspicious.

Post edited by: vic44139, at: 2006/07/12 10:08

Post edited by: vic44139, at: 2006/07/12 10:09

loose grounds have been known to blow fuses.

Here is what I think you should do...

First, the short is occuring in conjunction with the kill switch function. The fuse is blowing because of a short I think. Where would the short occur and blow the main fuse? Well, the power runs over to your ignition switch through a white wire and comes out on several circuits... brown, red, blue. The problem isn't the red which runs to the tail light but is in the blue or brown. If I had a better memory, I could remember but one of them runs TO the kill switch. Open your right switchgear and look. I think it is brown. If that is the case, the short will be between the brown out of the ignition switch and the right kill switch OR the brown likely tees and runs up to the LEFT HAND SWITCH GEAR and goes to your horn. It may three way tee; you will have to look at a wiring diagram but anyway, chase that brown wire on each leg of the tee... there is a bare spot that is touching the frame but I THINK you will find that the problem is associated with either the COIL wires or STARTER BUTTON WIRE! The reason is, that these are the wires that come off that brown wire in the right switchgear. The BLACK WIRE runs down to the starter button out of the KILL SWITCH and the YELLOW/RED wire goes off to power the coils. The BROWN going to the kill switch is HOT and when the kill switch is moved to the ON position, either the BROWN, YELLOW/RED or BlACK have bare spot in the insulation and touch ground or perhaps even another hot wire. When you open the switchgear you may have to take apart the kill switch and examine the wires inside the switchgear (colors I mentioned) carefully. If you see nothing wrong, trace down the yellow/red wire and black wire. Both run through the same big connector where the switchgear connects back into the main harness. That would be a possible short causer place as well. If you don't find the problem and if you have a dark place you can put the bike, take the tank off and put in a new 20A main fuse and watch these areas while you switch the power on and then the kill switch. There will likely be a spark as the short occurs.

Thanks for all the replies. I should have mentioned that I don't even use the starter. It's never worked all that great. I kickstart all the time. I rebuilt the kill switch last month so I tend to rule that out (Maybe that's teh best reason to rule something in, hahaha). The main part that stumps me is that it ONLY happens when I start the bike. If there was a an exposed wire somewhere wouldn't it likely short during a ride? The bike has NEVER shorted during a ride.

Please read what I wrote. The issue isn't whether you push the starter button... the issue is you turn the kill switch on. The problem is the kill switch, the wire from the kill switch to the starter button either touching a ground or another hot or the coil wires. Since the bike runs OK once going, I suspect the problem is the work you performed or at least inside the right switchgear.

there is a method of checking for a promlem such as this. short circut diagnosis
hook a test light in place of the fuse. you put one contact of the light where the fuse hooks in and the other lead to the other side where the fuse hooks in. right? as if the test light is the fuse, ok?? get a wire with clips on both ends it helps with the pointed tip

turn on power and start check connections plugs everything especially the chain of connections on ign circut. the test light is going to be the guide.

now there are three senerios
1 bright light = short circut (bad)
2 no light = turn the key on or no energy (bad)
3 dim light = good circut (good)

now while checking the light os using the electricity so lights and switches are not going to work. hope you find the problem