Topic: Blew three 15 amp fuses in a row.

[Mingo]

 Okay, while I'm still working on the issues noted in my two or three other active posts, I now have a new one.

I went for a 25 minute or so ride around town just now. After about 20 minutes of the bike doing well, and being nice and warmed up, I rolled to an intersection to wait for a red light and the bike died completely, all lights, everything. So I pushed it to the side of the road, checked the fuses and saw that the 15 Amp fuse was gone. I carried two replacements with me, so i put one in and it fired right up.

At the very next stop sign I let off the throttle completely, and let the Rpms drop to the 1800, or so, idle, and the bike died again.

I waited a while to see if a cooler bike would treat my last fuse any better. However, I was riding without my side cover, and the fuse area was not at all hot.

The last fuse got me home, but as I rolled into my parking lot, I let the revs die down and it promptly blew the third fuse.

Any ideas on what I should be looking for?

Bike is a '78 cb 750 K, with stock airbox, Kerker four into one, new plugs, new points. It's been timed recently and also had the valves adjusted.

[scottly]

Too many threads to keep up with.....
The main fuse blowing is due to either a red, or a black wire shorting to ground. The neutral light is supposed to come on when it's green wire is connected to ground. Any major cuts, damaged (melted) insulation in the wiring harness?

[Old Scrambler]

Check your points cover for a 'swinging' ground......if so, just loosten the wire connection to position the wire away from the metal contact.   

[Mingo]

Too many threads to keep up with.....

I know, right?  I'm not sure myself which ones are mine anymore.

Thanks for the info. That'll get me off to a good start tomorrow morning.

[Spanner 1]

You will blow 3 more in a row if you don't address your oxidised poorly conducting fuseholder(s).
The 'clue' in your post is that the bike quits @ a stop light ( motor @ idle ). At idle the bike is running off the battery and is at it's lowest voltage vs. riding down the road with the alternator adding 'charge' to the bike ( voltage ) and the load of the ign. and lights is at it's max. at idle = fuse melts  ....a really good upgrade is to change the fuses for auto type blade fuses... lots of info about that here.... good luck!

[lucky]

You will blow 3 more in a row if you don't address your oxidised poorly conducting fuseholder(s).
The 'clue' in your post is that the bike quits @ a stop light ( motor @ idle ). At idle the bike is running off the battery and is at it's lowest voltage vs. riding down the road with the alternator adding 'charge' to the bike ( voltage ) and the load of the ign. and lights is at it's max. at idle = fuse melts  ....a really good upgrade is to change the fuses for auto type blade fuses... lots of info about that here.... good luck!

Sounds like a good diagnosis  to me.

[Spanner 1]

Let's talk fuseholders...........again and again ( everyday on this Forum, just about ) a poster responds;
" the fuses all look O.K.'.... but the bike won't start/run and the lights etc. don't work.... ahem 
Any of our SOHC4 bikes are approaching 40 years old  and the fact that any of the electrical still works is very impressive ( without any maintenance ) ... stuff corrodes and needs to be cleaned, shone-up, snugged in their connectors and in particular the fuseholders need to be shone-up until they are all shiny brass colored and tyhe fuse holder clips carefully bent inwards to tightly grip each fuse.... 

[scottly]

You will blow 3 more in a row if you don't address your oxidised poorly conducting fuseholder(s).
The 'clue' in your post is that the bike quits @ a stop light ( motor @ idle ). At idle the bike is running off the battery and is at it's lowest voltage vs. riding down the road with the alternator adding 'charge' to the bike ( voltage ) and the load of the ign. and lights is at it's max. at idle = fuse melts  .

I don't think this is a case of an poorly conducting fuse-holder, Ray. With the motor idling, and the lower voltage, the load of the ign and lights will draw the least amount of current through the fuse. Ohms law.
I think this may be a case of a reversed battery/jump start type thing, melting the insulation off the green ground wire in the harness, as well as it's neighbors. This might be the cause of the blown fuses, as well as the intermittent neutral light. We'll have to wait for more input from the OP.

[Sdsbassist]

Brake light short perhaps?

[mronegear]

I fixed my corroded clamp of the main fuse 2 days ago. My bike wasn't dying. I just didn't load the
battery with the headlights on...

[Spanner 1]

At idle , without the benefit of of the charging system, the load across the fuse is at it's max.!
Say the headlight, ignition, taillight = 100 watts, then @ 12v ( and falling, without charge ) that's 8 amps. When the bike is running down the road and producing say, 14.5v then the load is 6.8 amps.
The load is the same whether the bike is at idle or at higher rpm ( and charging )....

[Sdsbassist]

Id still check taillight first. Same thing happened to me always making left turns. Had a stripped wire hitting the frame. Seems like everytime you stop, your blowing a fuse. Activiate your brake light with a 15 amp in and see if it blows. Start simple.

[Mingo]

You will blow 3 more in a row if you don't address your oxidised poorly conducting fuseholder(s).
The 'clue' in your post is that the bike quits @ a stop light ( motor @ idle ). At idle the bike is running off the battery and is at it's lowest voltage vs. riding down the road with the alternator adding 'charge' to the bike ( voltage ) and the load of the ign. and lights is at it's max. at idle = fuse melts  ....a really good upgrade is to change the fuses for auto type blade fuses... lots of info about that here.... good luck!

Is this still the case if my headlight is off?

Actually, that might be another clue. When I replaced my headlight yesterday (I'd had it off for a week or so), only the highbeams worked. So, if I didn't have the toggle on highbeams, I'd have no headlight. I kept the beams to low during the ride.

[Mingo]

Let's talk fuseholders...........again and again ( everyday on this Forum, just about ) a poster responds;
" the fuses all look O.K.'.... but the bike won't start/run and the lights etc. don't work.... ahem 
Any of our SOHC4 bikes are approaching 40 years old  and the fact that any of the electrical still works is very impressive ( without any maintenance ) ... stuff corrodes and needs to be cleaned, shone-up, snugged in their connectors and in particular the fuseholders need to be shone-up until they are all shiny brass colored and tyhe fuse holder clips carefully bent inwards to tightly grip each fuse.... 

Spanner, I'm just getting ready to go out to the garage and apply all this advice to my problems, but your comment about the fuseholder is interesting because I just sanded my three-fuse holder and bent the clips in--two days ago. I had a day where I was waiting for my MC rebuild kit and had nothing definite to do on the bike, so I sanded connections a bit.

In any case, the fuse holder is spanking clean--on the front. Were you referring to the parts on the back that I haven't seen yet? Should I take the holder off to clean it or is the fact that the leads/clips on the front of the holder mean that it might not be the fuseholder? Also, as I noted before, I had the headlight off.

[Mingo]

One more piece of information.

My front brake light switch does not work. The rear, pedal switch words, but the lever on the bars does not.

However, when I just went out there and starting testing it, i found that, with the motor off, but the ignition on, if I depress the rear brake pedal and then pull the front brake lever, the lights all dim. They dim when I pull the lever, not depress the pedal.

Could the fact that my lever brake does not trigger the light have some affect here?

[mronegear]

that is interesting! Did you pull the front lever just before the bike died at stop?

With Ignition on you have the Battery Voltage at the front break switch. If you press the lever you close
the circuit to the brake light and that might cause a shot to ground which will blow the fuse...

good luck!

[bollingball]

One more piece of information.

My front brake light switch does not work. The rear, pedal switch words, but the lever on the bars does not.

However, when I just went out there and starting testing it, i found that, with the motor off, but the ignition on, if I depress the rear brake pedal and then pull the front brake lever, the lights all dim. They dim when I pull the lever, not depress the pedal.

Could the fact that my lever brake does not trigger the light have some affect here?

Take out the brake light fuse and see what happens. These two circuits ( main & brake ) should not be connected unless your wiring has been messed with.
Ken

[Sdsbassist]

Maybe something hooked up backwards? Just had the same issue myself! Atock or aftermarket light?

Only reason I figures it may be brake/tail is because after my repaint same thing...

[Mingo]

Maybe something hooked up backwards? Just had the same issue myself! Atock or aftermarket light?

Only reason I figures it may be brake/tail is because after my repaint same thing...

Yes, the bike has new turn indicators. I put them on two days ago.

But why the inconsistency? I hit the brakes many times before the fuse blew.  And now in my garage, I can depress the brakes without blowing the fuse. 

[Mingo]

MORNING UPDATE:

I went out to the garage, put new fuses in and turned on the ignition.  Then I pressed the rear brake. Then I pressed the rear and front brake together and blew the fue.  I put another in and pulled both brakes and again blew the 15a fuse.  Engine is not running.

I went inside and posted about display lights dimming when I pull front brake lever.

I. Go back out to garage and look for red and black aeries that might short

I don't find any under seat, on frame or in headlight.

I. Do find a loose white male lead in headlight that sparks against a grind, so I cover it with shrink hose.

I can't get the side cover under the shift lever off as all screws are seized and many are stripped.

Now that i have jiggled everything around, I can't get the fuse to blow anymore, more do the lights dime when. Pull the brake lever. I found the leads from the f brake switch in the headlight and tried to make that work' but couldn't. The aback lead from that switch just sat in the headlight unconnected.  The greenish lead with a yellow line connected to a like wire in the harness. I tried to short the green/yellow line to grind to get the ligght to work, but nothing happened

I'm stumped.

[Sdsbassist]

Green is ground remember.

I think some typing errors in the last post are causing confusion.

1. Are you still blowing the fuse?
2. What issues still are concerning?

[bollingball]

MORNING UPDATE:

I went out to the garage, put new fuses in and turned on the ignition.  Then I pressed the rear brake. Then I pressed the rear and front brake together and blew the fue.  I put another in and pulled both brakes and again blew the 15a fuse.  Engine is not running.

I went inside and posted about display lights dimming when I pull front brake lever.

I. Go back out to garage and look for red and black aeries that might short

I don't find any under seat, on frame or in headlight.

I. Do find a loose white male lead in headlight that sparks against a grind, so I cover it with shrink hose.

I can't get the side cover under the shift lever off as all screws are seized and many are stripped.

Now that i have jiggled everything around, I can't get the fuse to blow anymore, more do the lights dime when. Pull the brake lever. I found the leads from the f brake switch in the headlight and tried to make that work' but couldn't. The aback lead from that switch just sat in the headlight unconnected.  The greenish lead with a yellow line connected to a like wire in the harness. I tried to short the green/yellow line to grind to get the ligght to work, but nothing happened

I'm stumped.

This is getting a little harder to understand.
Ken

[TwoTired]

Does the fuse get hot to touch before it "blows".

Does the fuse "Blow" near the center or nearest the end caps?


What are the sum differences in the bike's electrical equipment, between stock and what you have now?  Coils, head lights, etc.  Do you know how many watts you added to the stock power draw?

Does it still blow with a 20 A fuse used for temporary testing?

[mronegear]

To the frontbrake switch should be connected the Black wire for Battery plus and the green/yellow wire going directly to the breaklight on the rear.
So with Ignition on you must have +12V on the black wire at the brakeswitch. by pushing the lever black and green/yellow will get connected and the +12V will light the breaklight.

1. measure if you have that +12V at black wire at the switch
2. check connection green/yellow from front to the rear lights

[bollingball]

Mingo This problem could be related to others you have posted about. Like this one.

Also worth noting, maybe, that My clutch perch broke, so I bought an after market perch and just shorted out the circuit that keeps the bike from starting unless the clutch is pulled.
But you don't tell others about it in this post. When you say you shorted out this and that I'm not sure if what you call shorting means what others call shorting. You have hacked other circuits instead of fixing them correctly. I would suggest you back up and do it right. It is very hard to help someone when things like this are done. IMHO. No disrespect meant here at all.

Ken