Blown Fuse

If it's broken or just needs tweaked

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Chris
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Blown Fuse

Postby Chris » Fri May 12, 2006 11:11 pm

Hey guys. I did a bad thing today and I'm hoping you could shed some light on just how bad of a thing I did :) Last week while I was investigating the possiblity of replacing a missing screw on the face of my tachometer, I noticed that my instrument lights weren't working. The filiments in the bulbs looked fine so I checked the fuse and found it was blown. This fuse also belongs to the tailight which I hadn't noticed was out. I replaced the fuse with the spare and a few days later I noticed the tailight was out again. I didn't care so much about the instrument lights, but the tailight definitly needs to be working. So, last night I bought some more 10A fuses and this time I left the cover off of the fuses and began poking around the wiring harness with the ignition switch in the run position in hopes of finding the culpret. Everything was fine until I turned the wheel and the fuse blew :( So now I knew that the short was in the harness between the frame and forks. Just to be sure, I blew the rest of my 10A fuses in the same manner. When I looked in the cabinet for more fuses, all I could come up with was 20A. The 20A didn't blow and nothing caught fire. I'm really not a fan of disassembling a wiring harness and I couldn't find anyplace where I could disconnect the instrument lights only. So this morning I went to the store and bought a pack of 10A fuses and a pack of 15A fuses. I replaced the 20A with a 15A and it didn't blow and nothing caught fire. I also replaced the spare with a 10A. Do you think I did a really bad thing or maybe only nominally bad? It's so much fun finding out why I got my bike so cheap.
1980 CB650c

cb650
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Postby cb650 » Sat May 13, 2006 2:30 pm

Check wires going to the turn signals. the front running lites are are the same fuse and they get pinched in the turn limit tabs by the steering head. Might not be the prob but a place to start.



Terry

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Volker_P
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Re: Blown Fuse

Postby Volker_P » Mon May 15, 2006 1:44 am

Hi,
you were lucky to identify the origin of your fuse problem that soon. Presently the short seems to be not very strong but you should repair it anyway because of this:
With the 20A fuse, you probably got a spark at the short location which polluted the short surface for now. The layer will rub down soon and you will face the same problem again, possibly with stronger contact. Then you will need e.g. a 30A fuse and so on until you end up with serious problems (in the best case a blown main fuse). Most easy (and only reasonable) solution is to cut off the bad wire on both endings and pull a parallel one by hand.
Before you start, check the ignition lock switch first. The rear light is additionally switched with the parking light position of the ignition lock. This also may be affected by turning the fork. Maybe something is loose there instead of a wiring harness fault.
The instrument lights can be disconnected separately in one of the plugs inside the lamp. I inserted a switch as they blow quite often with time when riding with lights on also at daylight. But this would not solve the problem you described.

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Chris
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Postby Chris » Tue May 16, 2006 11:02 pm

Thanks Terry and Volker for the suggestions. It was doing fine with the 15A fuse up til tonight. When I started it up to leave work I noticed the taillight was out again. I checked the fuse right there on the spot, but it was ok this time and the instrument lights are still working. I'll check it out in the morning. I think maybe the 15A fuse allowed the short to blow the bulbs? Dunno, we'll see. As soon as I get the problem nailed down, I probably won't be able to wait until this winter to fix it, 'cause it'll drive me nuts til I do. I'll keep you posted.
1980 CB650c

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Volker_P
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Re: Blown Fuse

Postby Volker_P » Wed May 17, 2006 1:21 am

If instruments lights work and tail light does not, I would guess it is either related to the ignition lock parking position or the tail light itself. If you should have a small front parking light bulb, does it work?
Maybe I should ask first whether the US versions have this parking light stuff at all? :D

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Chris
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Postby Chris » Wed May 17, 2006 10:02 am

According to the electrical diagram that I have, the US versions didn't have the front parking light. Also, I noticed when the fuse was blown before that the rear parking light still came on with the ignition in the 'Park' position. Must be a different circuit. Gotta cut the grass this morning before I take a look at the bike, so I'll get back to you and let ya know what I find. Thanks.

-Chris-
1980 CB650c

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Chris
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Postby Chris » Thu May 18, 2006 1:07 am

Grrrrrrrrrrr! I've been all over this thing for hours and I still can't pin it down. I'm only getting 6v through the hot lead. I removed the ignition switch and cleaned the contacts inside. Still poking around with a meter. I'll let you know when I find something.
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Postby cb650 » Thu May 18, 2006 6:19 am

Electrics can be so much fun!




terry

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Vatch
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Postby Vatch » Thu May 18, 2006 7:00 am

Look at the bright side. At least you are working on a motorcycle and not crawling underneath the dashboard of a car. :D
'99 1500 Drifter

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Volker_P
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Re: Blown Fuse

Postby Volker_P » Thu May 18, 2006 9:31 am

Moreover it so far did not catch fire while passing a truck delivering fuel. :P

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Chris
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Postby Chris » Sat May 20, 2006 2:40 am

Progress!!! Does anyone have any idea why Honda would route 4 identically colored wires from the connectors inside the headlight bezel all the way down the harness to just behind the ignition coils underneath the gas tank only to connect all 4 together? :evil: ! It took me a freakin' week, but I finally found the short. There are 4 brn/wht wires that power the instrument lights/turn signal switch/tail light and God only knows what the 4th one is for. They run from 4 different connectors in the headlight bezel, down into the main harness and all the way back past the ignition coils where 3 are spliced into 1. Makes no sense to me, but that's where the wire is burnt in two. It's 3:40AM, I'm going to bed.
1980 CB650c

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rob
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Postby rob » Sat May 20, 2006 3:07 am

Makes me glad I haven't had electrical trouble with my bike yet :) Perhaps the wiring has been redone since it came from the factory?

Rob
'81 CB650 Custom

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Chris
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Postby Chris » Sun May 21, 2006 12:43 am

No way, Bro. This was the stock harness for sure. Hard to believe I know, but who else but the factory would do such a thing? Anyway, I cut out the short and soldered the wires back together. Then I put heat shrink tubing over it and taped the harness back up. Everything works fine now and I'm even back to a 10A fuse on all four circuits :wink: I still don't understand why those wires went all the way back there, but I only cut out the bad section to make the repair. I believe the cause of the short was that the harness passed under one of those hangers on the frame instead of through it and was rubbing up against it for 26 years. The wire probably burnt in half when I went to the bigger fuse. All's good now and I took it out for a couple hours today. Still can't believe I spent a week finding this.
1980 CB650c

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Ibsen
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Postby Ibsen » Sun May 21, 2006 1:42 am

Glad you found the short. :D

And don't beat yourself with it. Problems like this is the worst kind of problem you can deal with since they sometimes are very hard to discover. You did a good job. 8)

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Chris
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Postby Chris » Sun May 21, 2006 4:38 pm

Thanks, Ibsen. I wonder what's next this season?
1980 CB650c


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