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Locked Blown Fuse - Short Circuit
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Distinguished List Members,
I've enjoyed my 1974 R90S since 1996. It has been completely reliable throughout my stewardship and tolerant of my occasional neglect (as in not riding it for a few months). I have kept up on all routine maintenance and find that as many would agree, the tinkering and hands on maintenance is as enjoyable as riding it. It has about 56K miles on the clock. Recently after a short ride, I went to start the bike and found that there was no action at all when thumbing the starter. I also realized that although the power would come on when I turned the key (dash lights on, headlight works), the volt meter was reading "0". I suspected a blown fuse and confirmed that after opening the headlight bucket that the top 8 amp fuse was blown. I replaced the fuse and turned on the key which immediately blew the new fuse. I realized I was now dealing with a dead short. A quick review of the wiring diagram shows that the top fuse powers the flasher, ignition switch, brake light switches (front and back), volt meter and starter relay (am I missing anything?). Some initial trouble shooting showed that the right blinker wire had continuity to ground (this was easy to check and I had to start somewhere). When I disconnected that wire on the terminal block, I confirmed that that wire was not shorted (continuity was good through that wire but no longer to ground). I also decided to replace the starter relay just because it was easy and so many of the top fuse circuits run through that device. I plan on isolating the brake switches to remove them from the equation next. My question to the group is does anyone have any advice or experience that can shorten or focus my troubleshooting plan? Is there a common top fuse failure that you can share? Something that I should be focusing on? Should I treat myself to a re-wire given that the harness and all connections are 46 years old and I want confident reliability? What about those diodes on the back side of the terminal block? Could that be a likely point of failure? I appreciate the feedback. Thanks, Hans Kaufmann Oakland CA |
¿ªÔÆÌåÓýHans, I suspect your problem may be the starter switch, just a hunch.? Try cleaning the contacts on that switch, but be careful, there is a spring in there you don¡¯t want to lose. Good luck, Todd ? ? ? ? Distinguished List Members, |
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To debug a short circuit that blows fuses:
Using clip leads, attach a headlight bulb across the two tabs that hold the fuse. If there is a short circuit, the bulb will glow brightly, but nothing will be harmed. Then you can experiment with unplugging stuff until the short goes away (until the test bulb either goes out, or the intensity drops enough to notice. Bill Dudley |
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I second this technique. Works very well.
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To debug a short circuit that blows fuses: --
Joe Dille Telford PA What happens on earth stays on earth |
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Yes, it does work great. It is one of the methods I describe in my website for tracing
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problems. I have these set up to pass only 5 amperes or so, and maybe 1/4 ampere or so, etc. I also have both early and later type (style) of fuses, that blew out for whatever reason, fitted with wires and lamps, to use on such bikes having those style of plug-in fuses (Classic K bikes, etc.). Also the idea is very good for adding things like ammeters to measure circuit actual drain, etc.....especially useful when the current is far lower than a clamp-on meter will work well with. ETC. Snowbum -----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Joe Dille Sent: Tuesday, September 01, 2020 9:06 AM To: [email protected] Subject: Re: [R90SWORLDNET] Blown Fuse - Short Circuit I second this technique. Works very well. To debug a short circuit that blows fuses: -- Joe Dille Telford PA What happens on earth stays on earth -- Robert (Snowbum) Fleischer, Carson City, NV, USA ( ) ( ) ( ) ( ) ( ) ABC 1843; MOA Life 17058; AMA Charter Life 73254; USCA 6504¡.. ?(???)? |
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You can buy sets of these fuses prewired from any of the ¡°tool truck¡± guys.
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On Sep 1, 2020, at 1:35 PM, Robert Fleischer dba Fleischer's Service <snowbum@...> wrote: |