Topic: Overheating electrical circuit

[550Fss]

I have a 1976 CB550F ss in very good condition, less than 9,000 miles.  It runs very well, battery is only 2 years old and charges fine. It has been converted to electronic ignition.  The issue I have is periodically it was blowing the 15A fuse on the main power bus. I have tried tracing through the wiring looking for a short.  I did find a bare spot on the horn wire inside the lever housing. I cleaned it up and taped it off. Horn works fine. Could be a red herring. Now what I experience is the fuse does not completely melt apart, but the contacts and fuse are getting so hot the plastic is melting. The bike does not need to be running, just ignition on with an intact new fuse and it heats up.
 
I know from my wire diagram one lead goes to the ignition switch and the other goes off to power the rest of the bike. When the bike is running, I used my volt meter to read the voltage across the contact points that hold the fuse and only read 0.35V. Seems like I should have a stronger reading.

I am fairly mechanically inclined, but a bit challenged when it comes to the electrics. Hoping one of you folks might have some insight.  Thanks!

[69cb750]

Original coils and head light ?

[550Fss]

Headlight is original, the coils may have been replaced.  They look too new (I didn't replace them).

Found this from a site search, posted in a comment by TwoTired, could it be this simple?



http://forums.sohc4.net/index.php/topic,166603.msg1926459.html#msg1926459

Quote from: fr3ya on June 20, 2017, 10:51:29 am

    I'll also check the fusebox.  I did have a fuse melt to the cover a while back, but it was a fuse that sat in the bike, unridden for 8 years and after changing it I've had no problems.


The fuse clips develop a clear oxidation over time.  It's resistive and develops heat during use.  It can get hot enough to melt the fuse and/or the solder connections on the back side under driving conditions.  So, every ten years or so, you should polish off that oxidation so the contact area with the fuse is bright and shiny.  I use Semichrome polish, cause I have it, and is a very good metal polish.  Also, make certain that the clips grab the fuse with vigor.  Should need a tool to pry that sucker out.  Clean contacts and strong pressure keeps those fuse clips function almost indefinitely.

Cheers,

[scottly]

Most folks upgrade to a modern blade style fuse-box. Hondaman makes plug-and-play upgraded fuse boxes.

[Maraakate]

I had it melting quite a bit on my main fuse on my CB550.  I was unaware that Hondaman had a replacement box.  I just went to the local auto parts store and got a water proof blade-type fuse holder and switched it over to that.  I haven't blown a fuse or had to reseat it ever again.

I also tried cleaning it and pinching it down a bit tighter for the glass type fuse holder and it seemed to just bandaid for a little while but the problem would persist again.

[bryanj]

It is a known "old age" fault. Mark (hondaman) does a blade fuse conversion for these

[550Fss]

Hey, thank you everyone for the feedback, extremely helpful. I have done quite a bit of wire tracing lately looking for a culprit. I am going to first test out polishing and sanding the old one up.  If that works on the short term, I will definitely order up the Hondaman unit.  Looks like a nice clean way to upgrade.

This is why these forums are so awesome.  Thanks again!   

[American Locomotive]

If the fuse isn't blowing, then you most likely aren't overloading the circuit. Those old round fuse holders are pretty dodgy, and it's likely a bit of corrosion on the holder, or fuse causing heat build up.

[550Fss]

If the fuse isn't blowing, then you most likely aren't overloading the circuit. Those old round fuse holders are pretty dodgy, and it's likely a bit of corrosion on the holder, or fuse causing heat build up.

Like many thing on old machines, this one is a "tweener".  This all started out with random fuse blowing, minor to no heat issues. I could go 5-6 rides of 30-40 miles each with no issues.  The last few times after I lost all power to the ignition, the fuse looked unbroken, but I had heat and melting of the plastic housing.  I swapped the fuse out and was on my way.  One difference is, compared to when I had the fuse breaking, this is spring after a long winter storage.

I also just went for a ride after cleaning with metal polish and sanding with emery paper. I went for a 30 mile ride with no issues. The fuse position seemed mildly warm, but no melting. 

So I may have solved the corrosion leading to heat issue, but realize I still could have another underlying and random electrical gremlin leading to the fuse popping.  Only time will tell I guess.

[grcamna2]

I clean all ground connections from the harness,handlebar switches,etc. that go to the frame to Earth/common ground:it never hurts.I like that there is a better alternative to the stock fusebox from HondaMan. 

[Maraakate]

If you continue to use the original glass tubes then carry many spares.  Before I swapped it over to a blade fuse for the Main I would seem to have to replace the fuse every month or so.  If I didn't have to replace the fuse I would notice that sometimes I would put the bike on the center-stand when I would go to fill up and then take it off the center-stand, turn the key and nothing would come on.  I'd take the cover off and wiggle the fuse around and it felt kind of warm and usually things would come back on.

I also attempted many times to clean it.  Even with good stuff like De-Oxit.  The problems still persisted.

I finally got tired of this when I went for a drive at night and the bike shut off.  Luckily I was on a back road and not a highway and kept spare fuses.

Just get rid of that thing.  Continuously cleaning it and trying to make it grab tight again is just going to screw you later.  I'm lucky there was no traffic when this happened to me.  It was also pitch black, no lights.  Seriously, don't take the risk for it to be stock.  I'm usually pretty adamant about keeping things stock as possible; but nobody is ever going to look under your sidecover.  If you don't want to spend the money for the hondaman kit then do what I did and go to autozone and just get one of those waterproof in-line blade fuse kits and solder it in.

[550Fss]

Completely agree!  I wanted to run a test and make sure I didn't have another underlying issue (perhaps I still do, we"ll see).  My experience is very similar.  The two times it cut out while driving were on a back road or pulling into a parking area.  If in heavy multi-lane traffic, it could have been a bad scene. I am definitely going to replace the tube fuse setup with the Hondaman unit.  Even though this is an old bike in really good shape, I'm more about riding and reliability.

Ride'm, don't hide'm!

[BenelliSEI]

K7 and K8 cb750 are notorious for this problem. As the plastic melts, the fuse clips (that push in from the back) get looser. Looser = more heat, and the cycle gets worse.....

As a temporary solution, you can move the live clips DOWN  one space. The main feed gets to snap into the “spare” slot and you might get another 40 years out of it? Just remember to keep the top slots full of 15 amp spares!

[550Fss]

Just a follow up reply.  Purchased and installed the blade fuse setup from Mark (Hondaman). So far, working perfectly.

[grcamna2]

Just a follow up reply.  Purchased and installed the blade fuse setup from Mark (Hondaman). So far, working perfectly.

HondaMan has put together a very nice fuse box.

[bryanj]

One last point is that with electronic ignition your bike will only charge at higher revs than normal, probably need to be over 3500 rpm