Persistant Blow of 20A Main Fuse

(Forgive if already noted.)

What is battery voltage measured across the terminals ---
(1) ignition switch OFF;
(2) engine at idle;
(3) engine at 3000~4000 rpm?

Thinking maybe voltage regulator malfunction allowing battery to over-charge.

Just guessing here.

Good Fortune!

He's blowing a 20amp fuse and not the 10amp that feeds the instrument cluster/lighting inside the shell and such?

Hmmm, I guess anythings possible in a 30 year old KZ....

With all d-connected as in the red boxed image, can;t see how that is possible if still wired to OEM specs but considering PO wiring/bypasses... who knows....

Ignition switch connector goes through the grommet into head lamp shell? This would be white off of main fuse heading to Ignition switch, then out of switch to fuse panel sub circuits.

Old Man Rock wrote:

He's blowing a 20amp fuse and not the 10amp that feeds the instrument cluster/lighting inside the shell and such?

Good point: on mine, the main power comes through the ig switch and goes to the 20A fuse and feeds the ignition coil then goes to the two "sub" fuses of 10A each. Sounds like the short is on the front end before the smaller fuses.

Have you tried disconnection the coil power to see if it's a bad coil?

I might be mis-reading wiring diagram, but seems that 20 amp fuse feeds White wire into ignition switch, and turning ON ignition switch connects White wire to Orange/Green wire which doesn't enter the headlight shell, and also separately connects White wire to Brown wire which doesn't enter the headlight shell. (See image below.)

So much for my theory about a short inside the headlight shell as possible cause for blowing the 20 amp fuse.

This presupposes on bike at hand that the subject 20 amp fuse is located as shown on the wiring diagram. And that there's only one 20 amp fuse being used (to White wire) and that the other two fuses are each 10 amp.

If not already done, would confirm that the blowing 20 amp fuse is feeding the White wire that leads to the ignition switch.

Then trace for short in the Orange/Green from the ignition switch, especially at components fed by Orange/Green.

And also trace for short in the Brown from the ignition switch, especially at components fed by Brown.

Good Fortune!

[Click on image to enlarge view.]

Ah a picture of the contacts made by this models Ign switch.
Now if unplugging the connector at the switch, and making those contacts done by the switch with either the Tool I referred to before, or a home made version, see if you get a short. Do each one independently. Both the Orange/ green, and the brown will be under your seat as well. Brown ends up powering even your brake light switch, also starter solenoid, etc. Orange/ Green is turn signal, look at the flasher relay.

don't know if this will help
had a short on mine I traced it to a bad coil but when I went to remove the coil I found that where the wire hooks up to the coil it was touching the mounting post.
They are aftermarket coils.

eddiem wrote:

don't know if this will help
had a short on mine I traced it to a bad coil but when I went to remove the coil I found that where the wire hooks up to the coil it was touching the mounting post.
They are aftermarket coils.

Excellent suggestion!

Green Dyna 3 ohm coils for example have screw heads that may easily touch the coil mounting spacers.

Various options here, such as using non-metallic spacers, or insulating between the screw head and spacer, etc.

I use tie wraps around the oem spacers.

Good Fortune!

Exactly what I did

Hmmm. Guess which coils I have ...

I did notice that screw looked awfully close to the post.

@#$%, I bet you this is it.

And just like that, it lives. It was the screw of my Dyna coils grounding on the post. I wrapped that thing up tight with electrical tape.

Wow. And to think I rode the bike for so long before this became a problem.

Thanks to everyone who posted. What a relief it is to be back on the road.

Though with this being a vintage bike, I'm sure I'll be back soon.

For now . . . Victory Dance!!!

Patton wrote:

Green Dyna 3 ohm coils for example have screw heads that may easily touch the coil mounting spacers.

So that was it. But my bike sounds kinda strange. It doesn't seem to have the same amount of power. Could this have wrecked my coil?