Electrical problem

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Yellow_Cad

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At the tail end of a couple of hour ride my 73 mk I 850 blew a fuse just riding along. With the fuse out, I tested and have full continuity from the fuse holder (bike side not battery side) to any grounded surface on the bike and this is with the key off. I believe this shows that somewhere in the components or harness is a direct short. Can anyone give me some tests that might help isolate my problem? My electrical system and ignition system are totally stock. I did a search and only found a test for the rectifier by GrandPaul but was not real sure of exactly what to look for in this test. Thanks for any help on this.
 
There is no "short cut", you keep your meter at the point showing the short and start disconnecting stuff, when the meter shows open, then follow that branch. Keep in mind that the headligh being "on" will show low ohms, so will the points (if you have them) being closed.

Jean
 
If my key is off and yet I show continuity to ground, then what parts of the motorcycle are in question? Is the key switch in question in this case? Of the parts that are in play here, which show a direct short when faulty? Is the rectifier my most likely culpret? How should the zener diode read if good and if bad?
 
Yellow_Cad said:
If my key is off and yet I show continuity to ground, then what parts of the motorcycle are in question? Is the key switch in question in this case? Of the parts that are in play here, which show a direct short when faulty? Is the rectifier my most likely culpret? How should the zener diode read if good and if bad?
Click to expand...


The very first thing I'd do, would be to disconnect the wire from the Zener diode and see what happens, as there's a good chance it's the Zener at fault. The second check would be to disconect the "Blue can" emergency starting capacitor (if fitted?) ground wire. Third check would be to disconnect the rectifier output wire (Brown/Blue) if any of those tests doesn't identify the cause then it's probably a wire is shorting somewhere? .
 
Have a look at the wiring schematic diagram in your manual. Is it a "hard" ground - like 1 ohm or less, or just close to ground... how many ohms resistance are you measuring? Wiggle wires while watching your meter. Since it occurs with the key off that eliminates a whole bunch of the bike's wiring as the culprit. Use logic and a "divide and conquer" technique to isolate the problem instead of madly disconnecting all your wires. While you are looking, check for rubbing wires against the frame. One nasty area that I've seen myself is the blue can capacitor terminals rubbing the battery box.

This kind of problem is a pain. But if you approach it methodically and have patience you'll find it.
 
batrider said:
Have a look at the wiring schematic diagram in your manual. Is it a "hard" ground - like 1 ohm or less, or just close to ground... how many ohms resistance are you measuring? Wiggle wires while watching your meter. Since it occurs with the key off that eliminates a whole bunch of the bike's wiring as the culprit. Use logic and a "divide and conquer" technique to isolate the problem instead of madly disconnecting all your wires. While you are looking, check for rubbing wires against the frame. One nasty area that I've seen myself is the blue can capacitor terminals rubbing the battery box.

This kind of problem is a pain. But if you approach it methodically and have patience you'll find it.
Click to expand...


Batrider, that is exactly what mine turned out to be, a capacitor wire skinned by the battery box.
 
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