No ignition , blown battery fuse .

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Shelby-Right

Shelby-Right

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Just went out on the 73 750, got 5 miles and it died , no ignition light , found blown fuse at battery ,dead short to earth ,had to get my better half to drive my 86 F150 manual her first time, and pick me up , I am not electronicly gifted , so I searched on here which lead me to check continuity of zener diode , my multimeter went to 0.00 both ways , that's buggered I think? Can this diode cause the wiring to it to short to earth on the power side ? With the zener disconnected my power side battery wire go's to earth ! So need to find that .
So thinking about fitting the podtronics reg/rectifier , I have a boyer ignition , I have two wires out the back of the primary cover . I see the tri spark needs a different version not sure if it's required for boyer will ask british bike shop .
Cheers Vaughn.
 
To my knowledge the Zener diode should have a minimum of 10:1 front to back resistance, your
meter reading strongly suggests that you're correct.

The first thing I would suggest is, with key in your pocket, is to put 5 to 10 amp fuse in and see if it blows immediately. If this is the case, disconnect the Zener and try again, if you get the same result disconnect the rectifier and go again. If this still blows a fuse reconnect Zener and rectifier and disconnect the capacitor, try again. Still blowing fuses? Di connect all parts and try again. Last trial, disconnect the two wires that originate inside the primary drive, try again. While you are ding the trials take note of and wires that may be abraded.

Somewhere along the charging system trail you may gain enlightenment, but the coils, brake light switches and the may be bad actors.

If your wiring harness is original you'll be a good electrical tech by the time you catch and expunge the gremlins...then the frustrating process will start all over again.

Think about the purchase of a new harness, you'll be glad you did.

Best.
 
I have had the head light out to look for anything like a short, tank off , and zener off and still had earthing on power side of battery lead , I will go through it like you have said , thanks for that . Cheers Vaughn.
 
I recently had a short blowing fuses and giving weird tail light/brake light flickering with turns on. Turned out to be a short between a couple of lucar bullet connectors inside the 5 double multi connector. Insulating Rubber had split between two of the doubles right in the middle of the block. This was a new multi block and appeared from outside to be quite good condition.
 
That's good info , my big mulit block rubber under the tank main tube is pretty perished or splitting ,I will be looking and replacing it . Thanks for that .
 
Another quite common fault is a cable where insulation has worn off, grounding to chassis. Could be hard and very time consuming to find, especially if intermittent.
Disconnecting part of the system can help.
Fitting a light bulb in series with the battery will save a lot of fuses and tell you when you have removed the fault.
 
I had a fuse blowing short due to wear in my tacho light bulb holder. But only when lights on.
 
Shelby-Right said:
That's good info , my big mulit block rubber under the tank main tube is pretty perished or splitting ,I will be looking and replacing it . Thanks for that .
Click to expand...
When my new one shorted, I replaced with a few doubles and maybe a triple. These end up more manageable under the tank than the big 5 multi.
 
If all else fails and you do go down the route of a new harness, I can vouch for Wassells ‘Lucas’ harnesses and that is despite a couple of minor issues with 2 I’ve had - the connectors they use are very well made.
 
Naive question, but....
If you suspect your zener diode, is shorted can you just upplug it and them briefly see if the bike will run? And are you risking frying other components while it is briefly running without voltage regulation? Just thinking of a roadside check.
 
I think, as others have indicated, that it's some sort of wiring or connection problem that is shorting rather than the Zener. Re that, as I recall - been a long while since I did it - the procedure for checking a zener is different than the procedure for checking a standard diode but I might be misremembering...
 
Stephen Hill said:
If you suspect your zener diode, is shorted can you just upplug it and them briefly see if the bike will run? And are you risking frying other components while it is briefly running without voltage regulation? Just thinking of a roadside check.
Click to expand...
Doing this will cause system voltage to go too high (RPM dependent). If you have an EI it may kill it or hurt it. You can check the Zener as you have done with multi meter and engine at rest. I should have added that the leads coming from the stator should have continuity between each leg, but not to ground.

To the OP:
If you want to put this behind you get a new harness and a MOSFET reg/rec unit. If you find a short and patch it will just keep throwing rocks at you; this is, probably the best time of the year to be pushing a motorcycle...

Best.
 
FWIW, I few year ago I replaced the OEM Norton rectifier/Zener with a Podtronics and the result was .2V less voltage at every RPM than the rectifier/zener. At low/idle speed, this is the difference between charging the battery and discharging the battery. Don't assume that "new and modern" means it actually works better - or even as well - as the OEM stuff... ;)
 
Hi , I did remove it from the bracket and disconnect it , but still have continuity between power side battery lead (-) , and earth (+) frame etc , more investigation today , not able to hook up battery because of short .thanks for all answers i will read them all again this morning and try again to fault find it .Cheers Vaughn
 
30 or so years ago a friend of mine chased a similar issue for days. He completely removed the loom cut off all the tape and found nothing wrong. He re-wrapped it, put it on the bike and the issue was still apparent. He then started to unplug all ancillaries. As soon as he removed the stop / tail bulb the short disappeared. So check the simple things first. Also make sure the ignition switch is in the off position ;)
 
to answer your original question, yes, I believe a faulty zener diode can cause a short to power that blows the main fuse. I had the same issue when i acquired my current roadster 5 years ago. I don't remember the process (I think it was roughly that suggested by Road Scholar), but I isolated the zener as the culprit, replaced it, and the issue was solved. Running the original harness and charging system with a period Boyer Mk3. No electrical issues since. Got a replica Zener from Ebay. Think it ran about $50 US
 
Well after removing every bulb I still had a short on my power lead to earth , I did find some abraided wires from the brake switch after pulling them out and separating them , I seemed to have a partial fix , so with the zener completely disconnected and a small fuse in I got an ignition light and lights blinkers etc but the brown blue wires at the zener the rectifier and capacitor were all earthing and the earthing is coming from the blue capacitor . So with the brown blue and red earth disconnected from capacitor , across its terminals it has continuity, bad I think ? ? , I have ordered a podtronics unit . Comments on the capacitor would be great, I can weld and machine stuff but this electrical stuff is white man's magic ! .cheers Vaughn
 
The MC2 capacitor is not needed. It's purpose is to be able to start the bike without battery in an emergency. But big capacitors can trick you when measured with an ohmmeter. Initially they appear shorted until charged. A long measurement shall tell.
These electrolytic capacitors is polarity sensitive and will die when connected the wrong way.
 
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So to make it full discharged, put a light bulb across it ? , and when it's discharged should it have have continuity ?
 
In my experience, Zeners do fail into a short circuit. Taking the fuse out and stopping the engine is what happens.

I also found that riding with the headlight on ( not a legal requirement in the UK ) 'loaded' the alternator sufficiently to prevent it overcharging the battery / over-volting the RITA.

This is on a -ve earth T140 with a 3 phase alternator.
 
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