Topic: Wiring question

[Kenny39]

1977 CB550F Super Sport

Currently tracking down and cause for why my bike is melting the main fuse, looked around on the electrical section and found a rogue ground wire not connected to anything and unable to find an obvious connection to plug it into. Is there normally a green wire just hanging out back here? Bike can run and ride but after ten miles or so it dies, and is able to start back up again. It's pointing to an electrical issue, rectifier was a little toasty after a short test ride, and main fuse was cooked.

[denward17]

That main is getting hot.

How clean is the battery ground cable?  I would loosen it and check.

I would look for all the green (ground) connections and unplug/clean them.  Take out the headlight and have a peak inside the bucket and do the same.

[newday777]

Welcome aboard the forum Kenny39

Your pictures are showing dirty connectors as well as burnt fuse holder plastic in the fuse panel. You will need to clean all your connectors on the bike, dirt in any electrical connector causes resistance(heat) and need cleaning so you don't get further problems.
And I suggest you order a replacement fuse panel. Hondaman(site sponsor) has made up new ATC fuse panels to replace your bad panel, get rid of the old glass fuses that the inside soldered ends fail from age.

Fuse panel link, under site sponsors

https://sohc4shop.com/blade-fuse-holder.html

He is in process of finishing up a CB500/550 book to get released soon. He already has one on the CB750.

I'll see if I can find the thread on cleaning the connectors.

[rotortiller]

When the fuse contacts get dirty and corroded etc the resistance goes up and it heats enough to melt plastic. A good cleaning often fixes it and you can fill the melted hole sloppy with goop or silicone. You could by a replacement too.

[newday777]

http://forums.sohc4.net/index.php?topic=97649.0


https://www.focusst.org/threads/how-to-clean-heavily-corroded-electrical-connectors.160293/

For cleaning the round Barrel connectors
http://forums.sohc4.net/index.php?t17-Cal-Rifle-B

https://www.proshotproducts.com/17-Cal-Rifle-Bore-Brush_p_358.html

[Kenny39]

Thanks gentlemen, I have a solid set of remedies to try out now

[BenelliSEI]

The clips that connect to both sides of the fuse are tensioned by the slots in the plastic base. As they loosen, heat is generated and it just gets worse. A good short term fix is to move the clips to one of the “spare” slots. As others have suggested, replace it with a new one. Good for another 40 years……

[bryanj]

As others said replace the fuse box with one from Hondaman and the loose green is for a differnt blinker relay fitted in different countries

[rotortiller]

Fuse boxes are 25 dollars at https://www.vintagecb750.com/products/5/electrical/116/battery-fuse-relay and many other vintage Honda suppliers. I replaced one a short time ago and it fit great, it even came with spare fuses. Looks exactly like the original.

[bryanj]

Yup but they have the same problem as original. Hondamans upgrade kit is far superior and blade fuses are everywhere

[madmtnmotors]

As others have indicated, oxidized/corroded connectors are cumulative, i.e. each corroded connection adds more resistance on top of the corroded connection before it. I've done a couple of how-to's:

http://forums.sohc4.net/index.php/topic,137351.msg1549191.html#msg1549191
http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364

[rotortiller]

but they have the same problem as original.

If they see a bit of maintenance every decade the OEM will last forever.

[BenelliSEI]

Fuse boxes are 25 dollars at https://www.vintagecb750.com/products/5/electrical/116/battery-fuse-relay and many other vintage Honda suppliers. I replaced one a short time ago and it fit great, it even came with spare fuses. Looks exactly like the original.

+1 to that. If they last 1/2 as long as the originals, they’ll outlive me!

[Deltarider]

My bike is of 1976 and so far - in over 44 years of use by me - I have only had to address a faulty keyswitch and clean the main fuse clips. The V-4 measurement has proved all the rest is fine. Some connectors may look bad, but as long there's no V drop, I don't see the need to undertake all this 'maintenance', if that is what it is...

[Bodi]

I would measure the load current - just connect an amp meter in place of the fuse - to be certain there isn't an overload. A fuse should always be at or below 80% of its rated current.
But: the melted plastic screams bad fuse contact and overheating. Probably it's been hot enough to melt the solder on the wires underneath creating a bad contact there and even more heat.
It's a problem that snowballs once started. The original electroplating on the clips corrodes away unavoidably over time and by now it's long gone. So contact resistance goes up and a bit of heat is added to the natural heat from the fuse. That speeds corrosion of the clip base metal and the fuse end metal. Resistance goes up. Heat increases and possibly it starts arcing. Heat affects the "spring" of the contact metal, so it gets a looser grip on the fuse. Heat increases. Fuses start blowing but look fine, the solder in the ends attaching the fuse wire has melted. The plastic fuseholder plastic starts melting. The wires in back come loose with even higher resistance when that solder melts.
Moving the wires and resoldering them to the "spare" fuseclip is a temporary solution but good for now.
An aftermarket repro may be really good or may be a poor imitation. Replacements using modern blade fuses should be good but it's buyer beware.
I believe Hondaman Mark's fusebox is good. But I haven't tried it. I clean and inspect, maybe tighten the clips a bit,  my original 48 year old one annually and it's still OK although it has lost the original plating (Cadmium I think?).

[rotortiller]

it has lost the original plating (Cadmium I think?).

While I do not have one handy I thought the OEM fuse clip metal was solid alloy or something because after sanding, cleaning and polishing it came up clean and brass like under the fuse contact surface with no rust evident. If it's cad plating they did a good job! New and 50 year old fuse holder shown.

[bryanj]

There are two really common problems
1 people fit incorrect length fuses cos thats all they can get or they are cheaper
2 the heat produced by a poor contact at the fuse ends softens the clips and the loose their "springyness" making contact worse so more heat, plastic melts making contact even worse and i have even seen the soldered wire de solder and fall off

[rotortiller]

people fit incorrect length fuses cos that's all they can get or they are cheaper

How true and some guys are not smart enough to centre the correct length fuse in the holder. People can screw up the lord's prayer, that is provided they knew how it went lol. Look after the bike maintenance correctly and it will look after you.

[bryanj]

For several years correct glass fuses were very difficult to find, seems a lot better now