I have a 2001 sportster 1200 and I have a short that is causing the ignition fuse to blow. Started one day on my way home from work. Bike just cut out, so I called the wife to bring the truck and took it home. Found it to be a blown ignition fuse. Let a buddy convince me it was prolly just due to an old weak fuse. Replaced the fuse and fired right up. I then was on my way to an appointment and made it about 8 miles before it blew again. Called the wife and had her bring my fuses and a screw driver. 25 mins later I had a new fuse in and was headed back home. 4 miles later it blew again. Tried a new fuse and they would blow as soon as the kill switch was switched to run. So trailered it home where it continued to blow as soon as it was switched to run. Tried disconnecting the coil and a relay on the circuit. Still blew. Bike sat from the end of summer till recently with no attention due to a wedding coming and just not having the time or money to spend on it. Finally a couple of weeks ago I decide to get it going. Disconnected the voltage regulator and put another fuse in it and it didn't blow (also found a bolt missing from the regulator and fixed that since that's how it grounds). So reconnect it and it still doesn't blow. Let it run for roughly 20 mins and all seems good. Decide to go for a ride, figuring it was the bolt to the frame. Pull it out front and as soon as I pull onto the road and give her gas, she blew the fuse again. Was out of fuses so waited till this past weekend to mess with it. Got new fuses, put one in and it fired up with no issue. Ran the bike for 20 mins then ran it up and down the street and it never blew. Do the same today since it finally hit 60, run and put gas in it and start running, only to have it blow again. I'm prepared this time so I disconnect the voltage regulator, put a new fuse in. Doesn't blow, so I fire it up and take off. Make it 2 houses down and it blows again with the regulator disconnected. I'm completely stumped on this. Nothing has been changed or removed lately. Handle bars are original from when I bout it in 09, exhaust is 4 years old, carb work was done then, and the bobtail fender was done 2 years ago. So any ideas or a general direction to point me in would greatly help. I DON'T take my stuff to other people or shops and need to get back on the road.

 

Man, you gotta break that up into paragraphs, some of us have old eyes.

 

I have had two fuse issues. Neither same as yours. It took patience, good light, a lot of fuses but both turned out to me nearly microscopic bare spots touching the frame. Since I was not up to rewriting whole harnesses I found the rub spots and used flexible plastic sheets as insulators between harness and frame. Good luck. It worked for me.

Try to favor tracing the wire by color...that makes sense right? Since you were working around regulator and that postponed the fuse blowing a few moments longer I might suggest starting in that area with your search. Many years have taught me to look where I touched last when stuff goes wrong.

 

Verify the output voltage from the voltage regulator. You can measure across the battery with the bike running. Measure at idle and about 2K RPM's. It should be in the 14-15V range.

 

The voltage regulator has nothing to do with a fuse blowing. Too much current is being drawn by the ignition circuit. Probably a bare wire touching the frame.

 

Are you sure?? What happens to current when the voltage goes low?

 

If the voltage goes down, the current also goes down.

Ohm`s Law.

http://www.physicsclassroom.com/class/circuits/u9l3c

 

Agreed...now understanding Ohm's Law, what happens if the voltage regulator goes bad and the voltage goes higher?? I've seen bad regulators go as high as 18-20V.



The current will also increase. That's why I think he should look at the voltage regulator output.


I've been using Ohms law for more than 40 years. I appreciate your insight and I know you're only trying to be helpful, but I think you need to look at both sides of the problem.

 

I think you may be over thinking the issue (my problem is usually under thinking, or not thinking at all ).

A voltage regulator that is causing the alternator to overcharge the system will cause problems (like battery failure), but blown fuses is not one of them.

Even if the charging system voltage doubled, the ignition circuit would still not be carrying enough amperage to blow the fuse.

It is blowing one fuse, the ignition fuse.

The bike blew the ignition fuse as soon as the kill switch was set to run (the engine wasn`t running).

The problem is isolated to the ignition circuit.

 

I'm still having this problem and was about to take it to the shop when the guy was like (that's your ignition module). The way the problem arises (after it gets hot and then will start up without blowing a fuse when it cools off) it sounds similar to those issues caused by the ignition module, but is it possible for the module to be shorting out and blowing that fuse when it's breaking down from heat? It kinda seems possible to me if the diodes are breaking down and the current is allowed to be reversed but i have not seen anywhere that someone has had it cause a blown fuse. I've found no bare wires and have ruled out the coils, and voltage regulator.