Topic: CB500 fuse getting too hot when low beam on

[HS]

Finally got the old girl running and she's a ton of fun.  Engine's really strong.  Got her out and I opened her up and she died.  Turns out I blew the single fuse on the bike.  I have narrowed it down to the headlight.  If I ride with the headlight off, no problem.  If I turn on the low beam then the fuse gets hot in pretty short order.

Here are a few pics and thoughts....could use some input on next steps:

The hot spot on the fuse that I blew


The fuse holder clearly got hot on the same side as the fuse


The Stanley buld




And the Stanley headlight ring.  The bulb is made in the US (I think) and the ring is made in Japan so I'm wondering if it's the right bulb and can it be drawing too much???


I noticed the bulb seems to flicker or have a "wave" to it if I rev the bike.  Also, I changed out the right side handle bar controls that activates the headlight and starter with an aftermarket unit from David Silver Spares that seems to be working nicely.

I went through the headlight bucket connections for ground and the white wire and blue wire that controls the low and high beams and the green grounds as best I could.  They looked pretty clean to me but perhaps I need to clean them some how?  I applied some dielectric grease on some of them, especially if they were tight or looked the slightest bit off.  There was one green wire (ground) that had the slightest bit of exposed wire where the clear sheath that the female connector lies in had been pulled on but it is inside the sheath and no other wire nearby so I left it alone.

Thanks for any input.

Sam

[HS]

A bit more info...I recalled that the tail light is also lit in this situation.  I pulled a replacement bulb I used and the fuse was still getting too warm/hot IMO but not as hot.  I replaced the bulb with the original and no change.  Fuse definitely getting too hot with both the headlight and taillight on.

Sam

[Bodi]

Any headlight legally sold for US highway use has a DOT certification. I don't believe Stanley had any US manufacturing. The red stamp looks like Stanley to me, but it could be a US made lamp - the original was 40/50W and US sealed beam headlight lamps are usually 50/60W
The fuse hasn't blown but one end gets hot... that says you have a bad fuseholder contact. The fuse will blow if it's overloaded (assuming you have the correct amperage fuse!) Or (unusual) a bad fuse - but the burnt spot on your fuse looks like arcing to a bad fuseholder contact. You can clean up the fuseholder contacts and fuse ends and tighten the contacts a bit with pliers. Or replace with a modern blade type fuse block and fuse. Singles are available at pretty much any auto parts store or online.
The green wires in the harness can touch metal without any problems, all green harness wires are battery "-" and frame ground. Green wires from electrical devices (lights, horn, etc) connect to the harness wires - if one of these is not connected to a harness green the device won't work, and the wire can spark (harmlessly really, whatever it's from will flash or work intermittently) if it touches metal.

[HS]

Any headlight legally sold for US highway use has a DOT certification. I don't believe Stanley had any US manufacturing. The red stamp looks like Stanley to me, but it could be a US made lamp - the original was 40/50W and US sealed beam headlight lamps are usually 50/60W
The fuse hasn't blown but one end gets hot... that says you have a bad fuseholder contact. The fuse will blow if it's overloaded (assuming you have the correct amperage fuse!) Or (unusual) a bad fuse - but the burnt spot on your fuse looks like arcing to a bad fuseholder contact. You can clean up the fuseholder contacts and fuse ends and tighten the contacts a bit with pliers. Or replace with a modern blade type fuse block and fuse. Singles are available at pretty much any auto parts store or online.
The green wires in the harness can touch metal without any problems, all green harness wires are battery "-" and frame ground. Green wires from electrical devices (lights, horn, etc) connect to the harness wires - if one of these is not connected to a harness green the device won't work, and the wire can spark (harmlessly really, whatever it's from will flash or work intermittently) if it touches metal.

Thank you, Bodi.  I did take a way too large wire brush to the ends of the fuse holder, but I purchased a properly sized round set since purchasing the bike and I'll try those later today.  Perhaps replace the fuse holder altogether.  That's as logical a place to start as any.

Sam

[strynboen]

that  red vire at fuse hot end are shot..
..try to pull in the fuse holder..and hold in vire...im "shure "it breake just a few mm inside the red isalasion...heat means resisistens and a half broken/korodet vire gives heat...

[HS]

that  red vire at fuse hot end are shot..
..try to pull in the fuse holder..and hold in vire...im "shure "it breake just a few mm inside the red isalasion...heat means resisistens and a half broken/korodet vire gives heat...

Thank you, strynboen.  All I have done with the electrical is cleaned things up to get spark to all the holes, used dielectric grease where I can on connections and replaced the wiring that comes with the right handle controls.  Also the spark plug caps are new and fresh plugs.  I'm not very good with electrical so I shy away from it.  I will follow that wire as best I can without going too crazy and see where I can replace it without tearing the bike down too much.  Is that 14 gauge wiring on the red wire?

Sam

[TwoTired]

When joining two conductive media, connection pressure and or connection area is essential, in order for the electrons to easily jump from one bit to the other.

A fuse clip must not only be clean of impediments, but also grab very tightly in order to lower the resistance of the connection.  The lower the resistance, the lower the heating when current passes through the connection point.

Understand how a fuse performs it's function.  It melts when a certain volume of amps passes through it.  The passage of power through it's link resistance, heats the metal link to its melting point.  Slightly lower power transfer still heats the link, just not to the point of melting.

If you apply enough external heat, even with no current passing through it, the link will still melt.  If you heat the end cap, the heat will conduct into the link and effectively lower it current carrying melting point.  A 15 amp fuse can have an effective "blow point" of 10 Amps if it placed in an environment with external heat sources applied to it.  This is why the clips that grab the fuse must be clean, tight, and well fitting, so as not to lower the capacity of the fuse.

[HS]

When joining two conductive media, connection pressure and or connection area is essential, in order for the electrons to easily jump from one bit to the other.

A fuse clip must not only be clean of impediments, but also grab very tightly in order to lower the resistance of the connection.  The lower the resistance, the lower the heating when current passes through the connection point.

Understand how a fuse performs it's function.  It melts when a certain volume of amps passes through it.  The passage of power through it's link resistance, heats the metal link to its melting point.  Slightly lower power transfer still heats the link, just not to the point of melting.

If you apply enough external heat, even with no current passing through it, the link will still melt.  If you heat the end cap, the heat will conduct into the link and effectively lower it current carrying melting point.  A 15 amp fuse can have an effective "blow point" of 10 Amps if it placed in an environment with external heat sources applied to it.  This is why the clips that grab the fuse must be clean, tight, and well fitting, so as not to lower the capacity of the fuse.

That makes sense to me, TwoTired.  I'll hit the auto parts store today to see what I can find and start with replacing the fuse holder.  I'm using 15 amp fuses (replaced the original or whatever was in the bike when I bought it...it's a low mileage bike but obviously a few years on the old gal).

Here are a few pics of a bike with 6800 miles on it....1972 CB500 Four U.S model in case they are of use to anyone else or anybody sees any other issues.  I can say the wiring is pliable (easy to flex and not brittle).  All the bullet shaped connectors I pull apart look clean but that's not to say there isn't oxidation. 









under the seat




Sam

[HS]

So here is the back of my panel.  Anyone ever seen a green (ground) with no home like this one?  I can't see where it would connect to.






Sam

[wowbagger]

The spare ground is normal. If you ever switch to LED turn signals, you can use that ground wire on the 3 prong electronic turn relay you'll need.

[HS]

The spare ground is normal. If you ever switch to LED turn signals, you can use that ground wire on the 3 prong electronic turn relay you'll need.

Good deal.  Thanks, wowbagger.

Sam

[HS]

I removed the ring connector with the read heat shrink seen here connected to the round magnetic starter unit (that's what the parts list calls it).  There are actually two wires that go into that ring connector with the red heat shrink and one of them has one end of the fuse holder on the opposite end.  The thick black wire on top of it on the magnetic starter is the lead to the battery.


The ring connector and the read heat shrink removed and the electrical tape off...the fuse holder is the red line going to the right with the red dashed heat resistant material. 


I will replace it with the recommended fuse holder and fuse and see if that addresses the issue


Sam

[Bodi]

Note that the "dashed" insulation is because that wire carries unfused battery power. The extra protection is in case it rubs on some metal part - shorting that wire to ground would melt it pretty quickly and potentially start a fire. So be careful when installing your new fuseholder to have the wire from the solenoid well protected.

[HS]

Note that the "dashed" insulation is because that wire carries unfused battery power. The extra protection is in case it rubs on some metal part - shorting that wire to ground would melt it pretty quickly and potentially start a fire. So be careful when installing your new fuseholder to have the wire from the solenoid well protected.

Very good, Bodi.  I've got some heat resistant loom which I will use if it fits and if not, I'll use some add'l heat shrink/wrap to help avoid any excitement.  Thanks for the help.

I'm getting old and something occurred to me last night when I was working on the bike.  When I bought it, I thought the tail light bulb had gone bad so I ordered replacements.  With the new bulb not working, I traced the problem to the prior owner having unplugged the wire at one of the connectors under the rear fender, if memory serves me.  If this fuse holder/ fuse upgrade doesn't fix the issue, my next stop will be the tail light system...I should have thought of that before.  I'm wondering if perhaps that rear bulb wire is getting too much pressure/pinched where theres a mounting nut with rubber grommet on the rear fender and that could be creating the problem....

Sam