Author Topic: Main fuse keeps blowing (Read 25999 times)

Geeto67 · « **Reply #75 on:** April 23, 2007, 09:21:02 AM »

your fuse block is about to crap out. This is fairly common. It was probably vibrations at certain RPM and speed that caused the contacts to touch and blow fuses. Replace and see if it happens again.

Whenever you have a problem where the whole bike goes dead in an instant, start with the fuse block. It really is a piece of crap part.

Lumbee · « **Reply #76 on:** April 23, 2007, 10:50:51 AM »

...is there an aftermarket replacement out there for the fuse block...

KCs76Cafe · « **Reply #77 on:** June 10, 2007, 09:48:43 AM »

......over time.

Was going thru the wiring to try and find out why I was having problems with the main fuse. It doesnt pop at once...just over time it will get "tarnished" looking inside the right endcap...looking at the fuseblock.....then it will fail.

Was taking the battery out and noticed an old acid leak on the front part of the battery box...under where the vent is.....but I have the vent tube in place so I dont know why it would be on the battery box. So after I get the battery out, I noticed the acid had got down on the wiring harness plug coming from the stator. See pic below.....

Could this be my problem or should I look further? Going to the parts house now to get some electrical contact cleaner and try and clean some of this mess up. Will the contact cleaner get it out of the plug or should I use something else?

nickjtc · « **Reply #78 on:** June 10, 2007, 10:30:27 AM »

If there is any shorting happening in there you are going to have problems. Check the most visibly obvious places first before you start tearing your hair out!

canyon750 · « **Reply #79 on:** June 10, 2007, 10:36:32 AM »

The electrical cleaner will only put a band aid on the problem. It would be better to clean all the contacts by hand including the harness itself. But any amount of cleaning won't help unless you find the source of the acid leak. Remove the battery and completely clean the battery tray and surrounding area. Check the battery for cracks or loose fill caps (if you have a non-sealed battery). If its a sealed battery and its leaking then replace it. Once all the old acid is cleaned up (you are wearing gloves, right??) start working on lightly sanding those electrical connections with a super fine grit of sandpaper. Don't forget to work on the fuse terminals and battery connectors as well! While you're in there check for loose connections or damaged connectors. It will take a little bit of investigating but in the end your problem will be revealed..

TwoTired · « **Reply #80 on:** June 10, 2007, 10:57:52 AM »

Regardless of other woes with electrical, that connector needs an overhaul.

Use baking soda and distilled water to neutralize the battery acid spillage.

Examine the contacts and their connection points to the wires to determine metal volume loss due to acidic corrosion. If all is well, clean contacts to bright and shiny status, coat with dielectric gease, and reassemble.

I can't think of a senario where corrosion on that connector alone would cause the fuse to overheat. Unless the Vreg settings were also tampered with in an attempt to mask the real issue.

Cheers,

KCs76Cafe · « **Reply #81 on:** June 10, 2007, 10:58:39 AM »

I've got the battery and battery box out now. Just got back with supplies and getting ready to start cleaning it all up. Dont the wires/connects push out of the harness plugs? I figure that will be the only way to get all the crud out of the one pictured. The back of the fuse block looks good.....no corrosion and not real dirty but Im gonna clean it anyway.

TwoTired · « **Reply #82 on:** June 10, 2007, 11:01:13 AM »

The contact terminals have a barb that holds them into the connector. Compress the barb and the contacts will withdraw. Write down thier locations before you do, however.

Cheers,

KCs76Cafe · « **Reply #83 on:** June 10, 2007, 11:11:43 AM »

Crap.....I have no baking soda. Will white vinegar neutralize it? It 15 miles back into town

KCs76Cafe · « **Reply #84 on:** June 10, 2007, 11:16:50 AM »

Scratch that.....just realized vinegar is also acidic.

Back to town I go..........

TwoTired · « **Reply #85 on:** June 10, 2007, 11:30:31 AM »

No. Vinegar is another acid. Just not as strong as the sulfuric in the battery. Baking soda is alkaline. The pH scale goes from 0-14 with 7 being neutral or pure water.

Battery acid - pH 1
Vinegar - pH 3

Baking soda pH 8.5 ish

Baking soda was chosen because it is mildly alkaline. You can use a lot and it won't be very aggressive. Flush with pure water afterward.

Stong alkalines such as ammonia or lye will also conteract acid (violently). But, they are just as agressive at dissolving metals as battery acid!

I've never tried it but Milk of magnesia has a pH of 10. Wear saftey glasses.

Cheers,

liaudio · « **Reply #86 on:** June 10, 2007, 01:21:18 PM »

http://www.sohc4.us/forums/index.php?topic=20034.0

KCs76Cafe · « **Reply #87 on:** June 10, 2007, 02:15:54 PM »

I plan on doing that mod soon....I believe I will go with this one though.......

http://www.delcity.net/delcity/servlet/catalog?parentid=10899&page=1

canyon750 · « **Reply #88 on:** June 10, 2007, 06:17:30 PM »

I did that mod on my fuse box some time ago and it really cleaned up my fuse popping problem. I guess i'm a neat freak because I ended up attaching the fuse box where the old unit lived behind the sidecover. Check this link to the fuse box i used:

http://www.wiringproducts.com/

Click the Fuses and Accessoirse tab on the left and scroll down to this part:

4 Circuit Raised ATO/ATC Fuse Block

HondaMan · « **Reply #89 on:** June 10, 2007, 06:42:32 PM »

RXmanGriff was suffering a similar "intermittent fuse wearout" on his CB750F when he was here. It turned out to be caused by the wiring at the steering head, where several wires had cracked their insulation off and, if the head was turned to lock position, would spark momentarily. This would damage the fuse, which, after several more such events, would fail. The fuse also would develop a curious gold tinge from the series of events.

It was just a lucky moment when one of the other riders noticed the spark when Jerry turned the head while we were admiring his bike (it's a beauty!). The later CB750s had more wires going thru this area than the earlier ones, and it's a little tight in there.

KCs76Cafe · « **Reply #90 on:** June 10, 2007, 07:37:47 PM »

I'll have to check that area out.
Thanks for the info Hondaman.

Stumby · « **Reply #91 on:** August 22, 2008, 05:59:10 AM »

In regards to the main fuse melting the fuse box issue...

I've got a 75 CB550 F with this issue that has just resurfaced on me again.

Has anyone noticed (or maybe someone could check) that the wires coming off of the rectifier get very hot, even on the other side of the first plastic block connection? Could an old/bad rectifier be a reason for the main fuse blowing?

TwoTired · « **Reply #92 on:** August 22, 2008, 06:42:37 AM »

No.
The rectifier is not on the fuse circuit. It is directly wired to the battery.

Fuse clip oxidation is the usual culprit for fuse melting, along with headlight "upgrades" and low resistance coils.

Once the plastic melts and the clips lose their temper, it's like a snowball down hill.

If you can clear the oxidation from fuse and clips,
If the plastic still allows the clips to float so they can self align with the fuse.
If the clip metal still grabs firmly onto the fuse. (you should not be able the remove the fuse with your bare fingers.)
And IF the correct length fuse is used.
Then it can be reliable again. Otherwise replace the fuse box.

Wires getting hot is a sign of over current issues or connector heating (corrosion again). Is your fuse still 15 Amps? Or, has someone put a 30 in there to sidestep the real problem? What other electrical mods have been foisted upon the bike?

Has someone jumped the bike in the past and reversed the jumper cables?

Cheers,

Stumby · « **Reply #93 on:** August 22, 2008, 07:01:26 AM »

Quote from: TwoTired on August 22, 2008, 06:42:37 AM

No.
The rectifier is not on the fuse circuit. It is directly wired to the battery.

Fuse clip oxidation is the usual culprit for fuse melting, along with headlight "upgrades" and low resistance coils.

Once the plastic melts and the clips lose their temper, it's like a snowball down hill.

If you can clear the oxidation from fuse and clips,
If the plastic still allows the clips to float so they can self align with the fuse.
If the clip metal still grabs firmly onto the fuse. (you should not be able the remove the fuse with your bare fingers.)
And IF the correct length fuse is used.
Then it can be reliable again. Otherwise replace the fuse box.

Wires getting hot is a sign of over current issues or connector heating (corrosion again). Is your fuse still 15 Amps? Or, has someone put a 30 in there to sidestep the real problem? What other electrical mods have been foisted upon the bike?

Has someone jumped the bike in the past and reversed the jumper cables?

Cheers,

Thanks for the reply.

I can remove the fuse with my fingers, but no oxidation and the clips still seem to have a good grip on the fuse.

It's still a 15A fuse

A dip switch was installed to turn off the headlight. I'm bypassing it now, but I don't think this is an issue.

If it's not the rectifier me thinks the next culprit might be the solid green wires (4 or 5 of them) behind the fuse block. Or that is, the green wires that come out of all the plastic connectors in the area of the fuse block, between the air box and the wiring panel, have all been soldered together. One of the green wires has a female end with a clear plastic covering around it and is not hooked up to anything.

I guess I'm going to have to track down a good wiring diagram and figure out where those are supposed to go.

Stumby · « **Reply #94 on:** August 22, 2008, 07:18:24 AM »

Here is a picture...

http://jeffrey.smugmug.com/photos/356742682_iZRPK-M.jpg

TwoTired · « **Reply #95 on:** August 22, 2008, 07:44:08 AM »

Quote from: Stumby on August 22, 2008, 07:01:26 AM

I can remove the fuse with my fingers, but no oxidation and the clips still seem to have a good grip on the fuse.

Oxidation on these clips can be transparent and still resistive. Pass current through a resistance an it generates heat. If they haven't been cleaned in the last 30 years, it has oxidation.
Contact pressure on the fuse also effects resistance. More pressure = less resistance = less heating.

Quote from: Stumby on August 22, 2008, 07:01:26 AM

If it's not the rectifier me thinks the next culprit might be the solid green wires (4 or 5 of them) behind the fuse block. Or that is, the green wires that come out of all the plastic connectors in the area of the fuse block, between the air box and the wiring panel, have all been soldered together.

Well, that's a hack. But, it seems unlikely to be causal. BTW, Green is the Honda standard for frame connection or battery NEG.

Quote from: Stumby on August 22, 2008, 07:01:26 AM

One of the green wires has a female end with a clear plastic covering around it and is not hooked up to anything.

That's normal. Some countries require a three terminal flasher for extra lighting. The US isn't one of them.

Quote from: Stumby on August 22, 2008, 07:01:26 AM

I guess I'm going to have to track down a good wiring diagram and figure out where those are supposed to go.

Absolutely! Wire diagram is an essential tool!

Since you have hacked green wires, check the main frame connection up at the coil mounts. Clean those connections and inspect the green wire for signs of melting. When that one goes melty, it usually damages others in the harness on the frame spine leading back the rectifier.

You can always measure the rectifier with a DMM that has a diode test position, if you want to allay doubts about it.

Cheers,

Stumby · « **Reply #96 on:** August 22, 2008, 10:16:27 AM »

Thanks TT!

Cleaning off the fuse terminals seems to have made a difference. It's still getting rather warm, but not as hot as it was before. I'll be shopping around for a new one.

Any quick fixes on low gas mileage.

TwoTired · « **Reply #97 on:** August 22, 2008, 11:56:29 AM »

Quote from: Stumby on August 22, 2008, 10:16:27 AM

Thanks TT!

Cleaning off the fuse terminals seems to have made a difference. It's still getting rather warm, but not as hot as it was before. I'll be shopping around for a new one.

Any quick fixes on low gas mileage.

The fuse can be warm to the touch, but not so warm as to be painfull with your thumb on it. The fuse mechanism heats with current passd through it and melts when the curent exceeds rating. The main usually has about 10 Amps through it, so it's about two thirds on its way from melting through.

As for gas mileage. Replace your air filter. Paper ones are only good for a year.

Cheers,

beelsamin · « **Reply #98 on:** September 03, 2008, 07:31:13 AM »

I have a 1978 CB550 K in restoration.I've noticed that when I crank it over the main fuse gets really hot,so hot you burn your fingers.To my limited electrical knowledge this shouldn't happen,any area I should look at first to solve this?
Thanks

NGL_BrSH · « **Reply #99 on:** September 03, 2008, 07:34:23 AM »

you have too much resistance from corrosion would be my guess.

Clean the fuse holder, connecting wires and replace the fuse would probably do it.

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Author Topic: Main fuse keeps blowing (Read 25999 times)

liaudio

Stumby

Stumby

Stumby

Stumby