TOPIC:

I keep blowing the main 20 A fuse and I can't figure out why. Assume I know nothing... I have the wiring diagram but I really don't know how to read it.

I have good continuity from battery and starter relay to ignition switch (which passes through a fresh 20 A fuse).

Most recently it blew the moment I turned the kill switch to "run". So I checked continuity on all wires coming out of the kill switch:
-Good on the yellow/red to coil then coil to breaker points
-Good on the black to starter relay though both posts on relay gave continuity (Perhaps this is it? Those posts shouldn't communicate unless the relay is powered up, right? The relay did bench test well with a click and continuity between posts when powered up).

Would a crusty old regulator/rectifier cause a problem? Do I have a burnt out brake light switch? The lights do power on when the key is turned. Is it worth a newb trying to rewire from scratch or purchasing a whole new harness?

None of the rear lights are connected, by the way, but I also don't think they're grounding out anywhere.

Any thoughts?

Blowing the main is the hardest to trouble shoot as it's the main that powers everything . I would start by disconnecting head light blinkers etc one by one.

Are you in North Idaho?

South.

Start with this....

Have some spare 20 amp fuses....

See green arrows...
1) Dis-connect the the 4P connector to kill/start switch & Red/White conductor feed to the Regulator....
2) Turn on the ignition switch....
Fuse Blow again...?
If no, eliminates pretty much all electrical lighting circuits where problem lies in switch assembly itself (internal short)
or shorted ignition coil.
3) Turn off ignition switch.
4) Re-connect Red/White conductor connector feed into Regulator/Rectifier
5) Turn on the ignition switch....
Fuse Blow again...?
If yes then have a shorted Regulator/Rectifier
6) Turn off ignition switch.
7) Dis-Connect Red/Yellow conductor feed into ignition coil
8) Re-connect 4P connector into stop switch.
9) Turn on the ignition switch....
Fuse Blow again...?
If NO.... Then switch assembly not your problem of short.
Most likely shorted ignition coil or Contact /Breaker Points shorted capacitor for example in blue feed to ground
If YES Short in Switch assembly....

Your manual should provide a trouble shooting guide for resistance measurements ranges of a good coil

Hope this provides some starting points for you....

OMR

disconnect the front brake light switch.... had this happen on my 77ltd, when the front brake lever was pulled in as if stopped but slightly holding brake to keep from rolling it would short out and blew fuse.. did not blow when pulled in as to stop from a roll, or when lever not pulled at all. the front brake light switch is metal and directly screwed into metal.. the rear brake light switch is plastic, no metal, can't short out..

Hello all,
I just started having this issue yesterday and after some searching came across this strain and am hoping for some insight.

Here's the background.
While riding the other day the bike completely died on me out of nowhere so I started with the easiest thing and checked the battery which I found to be bone dry. I took it to O'Reilly's and of course it tested bad so I bought a new AGM battery. When I went to hook up the new battery (as much as I really hate to admit this) I didn't notice the posts were reversed and ended up hooking it up backwards. It arced a bit and blew the main fuse. I realized my mistake 2 seconds in and pulled everything off and hooked it up correctly, replacing the 30A fuse that was there with a 20A fuse that was shown in the manual, the bike then fired up and ran fine. I then tested the stator and was getting 14.5V at 4000 RPM like the manual said. I took it out for a test ride and about 5 miles in it blew the fuse again. I replaced the 20A with another 30A thinking that might be the issue. It ran for another mile or so and blew that fuse. I replaced that one with a 40A and it blew again as soon as I started the bike. I was only two miles from home so I bypassed the fuse and rode it home. Once home I started searching through here and found this strain and followed Old Man Rock's troubleshooting guide. Nothing listed in his guide made the fuse blow. The only things I have found is I can't get a reading when I try and measure the resistance of the Regulator/Rectifier. No matter which leads I test it always comes up 0. The other thing I found ( and it's really small) is that when I put the Vetter fairing back on after replacing the fork seals I had neglected to hook the horn back up and one of the leads had melted to the exhaust pipe. I have ran the bike with the 20A fuse in it and it hasn't blown, but I haven't had a chance to ride it yet. It also only reads about 13.2-13.4V across the battery at 4000RPM.

If anybody has any suggestions that would point me in the right direction they would be greatly appreciated. When it comes to electrical work I know just enough to get myself in trouble.

I apologize if i'm hijacking this strain a little bit but it seemed like my issue is relevant to the topic and I didn't want to start a whole new topic for a relevant problem.

See:
www.kzrider.com/forum/4-electrical/60377...r-threw-craps#741986

Still going strong, with no issue whatsoever!
Thanks again, Ed.

newjack213 Wrote:
I replaced the 20A with another 30A thinking that might be the issue. It ran for another mile or so and blew that fuse. I replaced that one with a 40A and it blew again as soon as I started the bike.

Egads - Why did you keep upping the size of the fuses? That's REALLY a BAD thing to do! The fuse is there to protect the wiring and other components. If you have a short circuit that causes too much current to be drawn the FUSE is suppose to blow. Otherwise the wiring or some other component will fry and possibly catch on fire. Installing a fuse rated at a higher amperage than the stock fuse can only lead to problems because you are circumventing the protection the fuse would otherwise provide. Don't do that! Ed

If you hooked the battery up backward, the rectifier could be damaged. However, if that were the case, the subsequent symptom would be the rectifier heating up as soon as the battery is hooked up... not necessarily a recurring blown fuse. But this possibility is not entirely ruled out. It depends on how the fuses are wired relative to the battery. So the rectifier is still a possibility even though it's not a likely possibility.

Since the leads on the battery are opposite of what they used to be, is it possible some wires had to move out of position from where they were? If so, maybe one of them is shorting against the frame etc. This is a more likely issue.

Incidentally, if the battery's positive post comes into contact with the frame. that is a dead short, (like if it moves from vibration or from hitting a pothole), but that type of short bypasses the fuses. The symptom is still that the bike dies, but it's the ground wires that start melting, rather than the fuse.

But another, and possibly the most likely issue, is that after the first fuse change, the fuse holder is no longer making as good of contact. This results in a lot of heat at the main fuse. This results in the fuse melting from heat, rather than blowing from over-current. It probably wouldn't matter what size fuse you use if this is the problem, as the heat source is the bad contact with the fuse holder, and not an issue with the fuse itself.

Check to see if the wires are discolored in or around the fuse holder. If so, try cleaning the fuse holders and give them a little squish to make them hold tighter.

Thank you all for your input. I haven't found anything grounded out from moving the battery wires to accommodate the switched posts. Earlier, when I started it after putting everything back together again the voltage across the battery spiked to 15V at 4000 RPM. The 20A fuse still didn't blow though. The excessive voltage is indicative of a defective regulator isn't it? I had put it together so I don't know if the rectifier is heating up. I will check on that next.

Over-voltage can be a defective reg/rec, but it can also be indicative of dirty connections leading to a reduced detection voltage at the regulator. The most common cause of that is dirty fuse holders.

Since you now have two symptoms of bad and/or dirty fuse holders, I think you need to inspect and clean/replace the fuse holders.