I am new to this great site, and forum. My 1971 KO Trail 70, owned since new has 1400 miles. Well maintained, and still like new, this is recently blowing the 7-amp fuse. The battery is correct, and new. With key on the horn will not sound as it used to. I apply 6.8V directly to the horn, it is LOUD! The motor starts fine. Tap the horn button, and I barely hear a groan. I have a good understanding of ohms, and circuitry. The bike now blows the hard-to-find BUSS BP/AGX 7A fuse. This trouble baffles me but I come back to the ignition switch as the horn used to sound with key on position, motor not running. Now, with key on, no horn. With motor running, depress horn button, I measure about .2 V at the horn; I get no horn sound. Thanks in advance. I know there are some really bright guys out there that are good with these issues. I don't want to throw new parts at this hoping the trouble will go away.
'71 CT 70 Blowing Fuses
- Thread starter mrfixit54
- Start date
Adam-NLV
Well-Known Member
Pull out the battery out of circuit and measure continuity from the Red (+) bat terminal to ground. It should be infinite 0hms. I'll bet your measurement is not infinite and probably read a short.
Sometimes this measurement will read Ok and when the bike is bounced around will read shorted; this is an intermittent problem and harder to locate.
Places that short are: the diode & connectors, ignition switch, brake lights and switches associated with that circuit. Remember on the K0, the headlight is AC and everything else DC.
Check the condition of that harness as it's really ooold too
OK, I am back. With battery out of circuit I have measured continuity from red (+) battery terminal to ground (I use the tail light bolt as ground). My Craftsman digital meter seems to be acting up so I am using my Calrad analog meter. Here are my readings. On the RX10 scale it reads: 7 or 700 ohms. On the RX1K scale it reads: 2 1/2 or 2500 ohms. It sure looks as though I have a bit of a short condition here.
I have done no further checking at this point. This is a learning experience for me. When solved I should have a great understanding of this system. Please tell me the function of, (see photo), what looks to me like a heat sink. Moving onto the stator, and rectifier will be new territory for me. Many thanks, Eric
I have done no further checking at this point. This is a learning experience for me. When solved I should have a great understanding of this system. Please tell me the function of, (see photo), what looks to me like a heat sink. Moving onto the stator, and rectifier will be new territory for me. Many thanks, Eric
kirrbby
Well-Known Member
That is your rectifier, and it looks like it's in very nice condition.
Your stator makes AC power. It has to be converted to DC power to charge the battery. That is what the rectifier does.
The headlight is not powered by the battery. It uses AC power straight from the stator. Your bike has 2 different circuits for lighting. The lighting coil is "center tapped"... basically split into 2 circuits.
Your stator makes AC power. It has to be converted to DC power to charge the battery. That is what the rectifier does.
The headlight is not powered by the battery. It uses AC power straight from the stator. Your bike has 2 different circuits for lighting. The lighting coil is "center tapped"... basically split into 2 circuits.
Adam-NLV
Well-Known Member
Just to double check; I pulled the red bat terminal off the battery and measure continuity on my 91' CT70 and just like I figured it is infinite 0hms or an Open circuit like it should be. Any other measurement, however small will either blow the fuse (as in ure case) or just drain the battery.
Sounds like you have a pretty good short. 700 0hms is real close to a dead short. Your gonna have to find out what is pulling it down. With your meter measuring 0hms, start down the line and find where the short is. your gonna need a wiring diagram and a reliable meter. I use a professional FLUKE 806A digital multi meter and it's very accurate.
That part in your pic is a old fashion diode, I think it's selenium. An old part and very low tech. It does fail, so check around that component. Good luck.
Sounds like you have a pretty good short. 700 0hms is real close to a dead short. Your gonna have to find out what is pulling it down. With your meter measuring 0hms, start down the line and find where the short is. your gonna need a wiring diagram and a reliable meter. I use a professional FLUKE 806A digital multi meter and it's very accurate.
That part in your pic is a old fashion diode, I think it's selenium. An old part and very low tech. It does fail, so check around that component. Good luck.
kirrbby
Well-Known Member
IME blowing fuses = a short. My first thought is the brake light switch wires at the foot pedal, right where they enter the frame. Maybe where the wires exit the frame going out to the taillight. Unplugging the horn would be a easy check too. Remove the TL bulb for another check...maybe the bulb is bad.
cjpayne
Well-Known Member
The fuse blowing all the time is a sign that you have a short or surge happening. I would unplug the headlight until you have found the problem. I learned the hard way that if you don't have a good battery, rectifier, or fuse, the headlight will blow just after a few minutes or so when turned on. These bikes have a "balanced system" that uses the battery as a voltage regulator. There is a colored K0 wiring diagram in the Resources/Links section of this forum http://dratv.com/noname162.html .
darrel gunderson
Active Member
Has the ignition switch been changed by chance? I have seen more than once, a K1 switch installed in a KO bike and its a direct short that will blow the 7amp fuse when you turn on the switch? Also have seen it melt the green ground wire where the harness plugs into the ignition inside the frame......
Adam-NLV
Well-Known Member
Just to clarify...my measurement was with the key off, that's when an infinite 0hm reading was read.
With the key On: The continuity measurement reads low, like <10 0hms. That is reading the filament of the neutral light bulb, (which illuminates with the battery in circuit & key on, bike in neutral)plus taillight filament too. And...I also have some running LED's in circuit too.
It's really difficult troubleshooting electrical problems over a forum but if your bike started blowing fuses constantly, there is something shorting somewhere that needs attention quick.
With the key On: The continuity measurement reads low, like <10 0hms. That is reading the filament of the neutral light bulb, (which illuminates with the battery in circuit & key on, bike in neutral)plus taillight filament too. And...I also have some running LED's in circuit too.
It's really difficult troubleshooting electrical problems over a forum but if your bike started blowing fuses constantly, there is something shorting somewhere that needs attention quick.
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No, my ignition switch has never been touched, it is the original; thanks for that suggestion.
My Ohms reading was taken with the key off. Troubleshooting VIA this forum has been very helpful to me; you guys have been terrific with your help! With Thanksgiving in the mirror I hope to dedicate more time to my old Honda... once I finish the installation of a new Burnham oil-fired boiler that is... I will keep you all posted.
My Ohms reading was taken with the key off. Troubleshooting VIA this forum has been very helpful to me; you guys have been terrific with your help! With Thanksgiving in the mirror I hope to dedicate more time to my old Honda... once I finish the installation of a new Burnham oil-fired boiler that is... I will keep you all posted.
Wow, It is now over two years since I started this post. Sadly, I've had little time to devote to this great old Honda and the shorting condition; but now I am finding time and determined to get to the bottom of this.
With battery out of circuit, ohm meter connected to red (+) wire at white battery connector, and grounded, here is what I find. I still have 700 ohms resistance. At this point, fuel tank removed, I wiggled every wire I can reach...Upon wiggling the four wires that enter the battery connector, (red, blue, two black) the ohm meter repeatedly moves and often goes to infinity, open circuit as it should read, alas! I think I have isolated the possible short. I carefully removed the first two inches of plastic wrap around the four wires but see no wire jacket wear at all. Oddly, I can now no longer get the ohm meter to move off of the 700 ohm reading! See photo... I have inspected the harness and see no cause for alarm... This bike was and is always stored well (no mice), was never abused, and has but 1,400 miles. I am thinking toward the idea of possible corrosion growing somewhere causing this short. I don't have the luxury of another bike to compare, and worse, I am not as knowledgeable as all of you great viewers.
I have printed all of your terrific suggestions and replies to my original post. With these to go on I am digging in and will keep you all posted. Many thanks once again...
With battery out of circuit, ohm meter connected to red (+) wire at white battery connector, and grounded, here is what I find. I still have 700 ohms resistance. At this point, fuel tank removed, I wiggled every wire I can reach...Upon wiggling the four wires that enter the battery connector, (red, blue, two black) the ohm meter repeatedly moves and often goes to infinity, open circuit as it should read, alas! I think I have isolated the possible short. I carefully removed the first two inches of plastic wrap around the four wires but see no wire jacket wear at all. Oddly, I can now no longer get the ohm meter to move off of the 700 ohm reading! See photo... I have inspected the harness and see no cause for alarm... This bike was and is always stored well (no mice), was never abused, and has but 1,400 miles. I am thinking toward the idea of possible corrosion growing somewhere causing this short. I don't have the luxury of another bike to compare, and worse, I am not as knowledgeable as all of you great viewers.
I have printed all of your terrific suggestions and replies to my original post. With these to go on I am digging in and will keep you all posted. Many thanks once again...
At this point, given that info, I'd pull the harness from the bike, unwrap it and check every lead. I seriously doubt that you have a keyswitch problem, those are vanishingly rare anyway. OTOH, broken leads are commonplace. The most common location(s) are between the frame & headlight bucket...which doesn't mean "exclusively".
I've gone through a number of these wire harnesses that appear to be intact when, in fact, there's a break covered-over/hidden by the insulation. Wiggling the leads and seeing a difference is classic, as in "textbook" manifestation of a broken lead. Best guess, it's the switched DC (battery +) lead that feeds the horn, brake light and speedo backlight. The headlight & high-beam indicator are fed AC, only when the engine is running.
I've gone through a number of these wire harnesses that appear to be intact when, in fact, there's a break covered-over/hidden by the insulation. Wiggling the leads and seeing a difference is classic, as in "textbook" manifestation of a broken lead. Best guess, it's the switched DC (battery +) lead that feeds the horn, brake light and speedo backlight. The headlight & high-beam indicator are fed AC, only when the engine is running.
Thanks ever so much racerx. I will print your reply, put with my info and check everything that you suggested. I will also post my success that I one day will achieve.
I am back to report on my success.
Knowing the red battery wire is shorting, with ohm meter connected to the red battery wire, the other end to a ground I was still reading 700 ohms resistance when there should be open circuit. I began to gently wiggle the four wires entering the headlight bucket, when suddenly I finally got some movement on the ohm meter! The meter moved to open circuit, now there is no short and it never changed! I disconnected all wires in the headlight bucket, then cut to remove the shiny black jacket running from exterior tunnel to bucket I inspected each of the four wires there...all like new, only dusty.
I reconnected each wire in the headlight bucket and continued to watch the ohm meter. No matter what, that wire no longer shows any sign of a short. With fuel tank and battery installed, I placed a new fuse, turned the key, honked the horn and I am back to normal! A loud horn sounds when only a soft groan was heard with that shorted wire.
Go figure? I will now know where to turn if this ever occurs again. For now I can polish and service my little gem.
Many thanks to all who helped out!
Cool biz! But, I'm a little less than resting easily. Electrical short circuits don't just heal themselves. Assuming that you pulled on all of the leads, to check for hidden breaks and found none. That means there was a (+)-to-ground short somewhere. Could've been anything from a single pinprick in the (+) lead to an errant metal fragment at one of the connectors, even the reverse side of the keyswitch. You could be truly good-to-go and that's where my apprehensiveness lives "could" is not a guarantee. That said, there is more than one upside to this. First off, there's a fair chance that the problem won't return. Second, worst case, you'll go through some fuses...no meltdown...and then make corrections.
Anyhoo, glad to hear that you're up & running. Go put some miles on that machine.
Anyhoo, glad to hear that you're up & running. Go put some miles on that machine.
