Persistant Blow of 20A Main Fuse

78 KZ650 D1

I started a thread about this a while back but haven't been able to work on things for a while. I figured I'd start a new thread because so much has changed since the first post.

My main 20A fuse blows as soon as my bike warms up. I fire up the bike and without touching it at all, the fuse will eventually go after about 2 minutes. If I replace the fuse immediately after that and try to start the bike again, the fuse will blow instantly. Sometimes it blows as soon as I turn the ignition key but this is only after the bike has warmed up.

Due to scorch marks and excessive heat (will burn your fingertips) around the connections to the reg/rec, I thought maybe I had a bad reg/rec. A couple people told me to unplug the reg/rec and see if the fuse still goes. So I did that, the fuse still went.

This leads me to believe there is a grounding problem elsewhere, though, I have searched high and low on this thing without any luck. I've opened up the controls and headlamp almost a dozen times, no exaggeration, and can't see anything.

Is there anyway to use a meter to track down something like this? I feel like I'm just shooting in the dark here.

You have to isolate circuit branches. For example, warm it up and shut it off. Then remove the red wire that feeds the coil and turn the key on. If it still blows, It's not the coil. Disconnect the headlight, etc. Try to find something that when disconnected, keeps the fuse alive.

What it can be is wires in the harness that got stretched rubbed through the insulation and can ground out. Those are pretty common

Incase you need.... KZ650 web site dedicated to 650's....
Wiring Diagrams...

diagrams.kz650.info/wiring/WiringDiagrams.htm

2 thoughts come to mind in your situation,,,, but first, to blow open a fuse whether heat, electron flow all that theorhetical down to earth scientific theory of applied science, keep it simple... Excessive current through that fuse blows the fusible link....

With that said.... in your case may be explainable but screw that....

If blowing open after 2 minutes, you're most likely drawing close to the 20 amp range right off the bat... After a couple minutes it just gets so damn hot it blows the link open.....

Or..... after a couple of minute warm up period, something on the load side of the fuse (non regulator side) takes a direct dump to ground....

As can be downloaded from the provided site for your KZ model, if that drawing is correct, the regulator could crap directly to ground and that fuse wouldn't give a rats ass for that is a direct feed into the battery (+) :blink: ....

Try this.... Disconnect everything for bare bone minimum operations....

Stater/Dynnamo, Vdc Regulator connected as designed, feed the +12Vdc into a inline 20 amp fuse then a 20 amp on/off single pole/single throw switch... The switch out put is your feed into the coils RED/Yellow conductors....

If you have a Dyna ignition, also switch +12Vdc to it...
Even disconnect the starter and use the kick start... INsure your feed back for charging the battery is connected but d-connect everything else.....

Now run your test... fuse blow yes/no....

If no, then one at a time start plugging in your other connections... Example, start with d-connecting everything but what you just had in a bypass off the ignition switch...

Otherwords, battery to 20amp fuse to white conductor up to ignition switch... Jumper switch outout to coils only... Test... Blows Yes/No...

Then re-connect lights or brake stop light what ever... Basically one at a time... until you find the one connection that blows the fuse... chances are it;s in the instrument cluster/head lights....

I realize this is somewhat confusing so I'll STFU now....

As a side question, is it normal for the two yellow wires coming from the alternator to the reg/rec to be super hot? And if so, could they be getting hot as a result of anything other than the alternator?

Confusing??? Naw. I know what u were trying to say and I read it and it made perfect sense to me--but of course I'm in the rubber room at the old farts home right now so everything makes sense to me,including this little cocka rocha Ive been talking to for the last few minutes.Beeba-bubba-booba-bumble.bj

In all seriousness,get some spray electrical cleaner and clean the fuse contacs on the fuse block as well as the wiring contacts that attach to the fuse block.They do get corroded.bj

I'll mention that I have swapped out my fuse box for mini ATO blade type fuses.

Good point BJ... One better, replace them old fuse clips with these....

BTW "Beeba-bubba-booba-bumble."... Spewed my Dr Pepper... :laugh: :laugh: :laugh:

Yeah I'm rocking those already. Good stuff.

You have a DVM capable of DC amperage measurements?
May provide some answers....

Yeah my meter can do Amps DC for sure.

Can you elaborate on what I should do with that. I'm pretty new at this stuff.

Measure on a cold start your current draw...

~8-9amps or are you pulling ~ 18-20amps right off the bat.....

If at the latter, turn off the engine immidiately and start disconnecting one at a time your electrical harness connections until you find it drop ~ 9amps....

See if your on the extreme high side right away, would explain why your Stator wires are hottter then normal....
Meaning your over taxing the AC generation due to a short/faulty....