Voltage drops to 0 when turning key on

Hi all!

I have a strange problem. When key is off, the voltage on battery with the multimeter is at 13.4 . After multiple check on the bike : frame, engine, etc, the voltage is at 13.4.

When I turn the key on, the voltage drops to almost 0 everywhere, except on the battery. Any idea?

Regards

Ignition switch ???

Poor connection. Keep doing voltage readings as you work AWAY from the battery, at every connecter. The female bullets ALL suspect...

polarity correct?

Negative or positive ground?

Deets55 said:

polarity correct?

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Well you would smell it if it wasn't correct or your wiring be toast.

13.4 seems high for a non Li battery, but 0 volts when the ignition is clearly an issue, but do check your meter with some known values.

With the ignition key in the first position you are energizing the ignition circuit, the brake light circuit, the horn and the directional circuits. Disconnect the power to each circuit (one at a time) until you find the offending circuit, which you can then check the sub sections of that circuit.

Failing that:

As mentioned earlier check your connections for abrasion (visual) and your ignition switch for contact to ground (battery disconnected). A 40+ wiring harness doesn't owe you much.

Failing that:

Go through the charging system. I had a similar issue and found that one of the diodes in my rectifier had given up the ghost; I found this by doing a front to back resistance check on the rectifier. The front to back should be at least 10:1, probably more. Check also the zenner diode you should see similar results. While you are at it check the stator to insure that neither lead has direct continuity to ground and that both (all) leads have continuity between each other.

Norton electrics are fundamentally simple, which insures that frustration is, generally, close at hand. A little Zen helps a lot....Be the ball....

swooshdave said:

Negative or positive ground?

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Positive ground.

Thank you all. I will check all the connectors from the battery to the end.

Have a look at the connectors shown halfway down here: bad-alternator-regulator-diodes-t23426.html?hilit=connectors#p308197
All HIDDEN inside the rubber... singles, doubles, triples... they ALL do it

I recently had a fuse that ohmed good, visually looked good, but wouldn't flash the turn signals on my vintage DT400. Turns out the element was unsoldered from the end cap, made SOME contact.. but NFG, check carefully. Also, the fuse holders can be dodgy, weak spring, etc.

phliper said:

When I turn the key on, the voltage drops to almost 0 everywhere, except on the battery.

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"Almost 0 everywhere" is rather vague?

Could you give a more detailed description of one (or more) check(s) where this is happening (+ & - probes, connected where?)?

There shouldn't normally be voltage in the switched side of the electrical system "ignition OFF", so I don't follow where you are measuring volts, with the ignition OFF which then drops to around zero when the ignition is switched ON?
A voltage drop as you describe, that occurs when the ignition is switched ON sounds like you could be checking between 'unswitched'(battery) and 'switched' negative wires?

No volts in the system when the ignition is switched ON would obviously result in nothing working (no lights, horn etc.) so is that what's happening?

Open circuit via the switch or lack of cct back to battery.

Undoubtedly you've got a high resistance item in your circuit somewhere. Good culprit is any switch, or connection. If you can get to the wires, measure across each connection or switch and most likely somewhere you will measure the 13V. That's the bad one. Or you could just start cleaning all your connections. I had this happen to my ignition switch a couple years ago. Switch looked fine, but when it was on, all the voltage was across it, nowhere else. Cleaning and de-ox fixed it. You probably won't be able to read the high resistance with an ohm meter either, it takes current for it to show up.

Have you looked at your battery yet ?

I had a battery that seemed healthy enough, but one day I turned the key on and noted that the warning light seemed very dull.
Under load, that battery was suddenly a (very) dead duck.

DogT said:

Undoubtedly you've got a high resistance item in your circuit somewhere. Good culprit is any switch, or connection. If you can get to the wires, measure across each connection or switch and most likely somewhere you will measure the 13V. That's the bad one. Or you could just start cleaning all your connections. I had this happen to my ignition switch a couple years ago. Switch looked fine, but when it was on, all the voltage was across it, nowhere else. Cleaning and de-ox fixed it. You probably won't be able to read the high resistance with an ohm meter either, it takes current for it to show up.

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Thank you! I redone my entire wirering with a new one. So i will check each connectors. My rear light works, but not the other. So i guess that's what's draning my power.

Rohan said:

Have you looked at your battery yet ?

I had a battery that seemed healthy enough, but one day I turned the key on and noted that the warning light seemed very dull.
Under load, that battery was suddenly a (very) dead duck.

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The battery is brand new from this summer. What could tell me if it's faulty?

I had a battery that was one week old go kaput 1500 miles into a 13,0000 mile cross country trip. It read 12.3 volts at the terminals. Under a load the battery dropped to near zero. I disconnected the battery and connected the leads to a cars battery using jumper cables. Max voltage again. New doesn't mean good. When I worked for BMW motorcycles we had more than one case of battery failure right on the showroom floor. This was on bikes that had battery tenders rotated among them. BMW sent a stern warning to the battery manufacturer.

phliper said:

What could tell me if it's faulty?

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If you could wire it temporarily directly to the headlamp, and verify that the headlamp puts out a good strong light.

If that is so, then you need to chase through all the connectors, as mentioned, and find one that isn't a good connection.
Including the fuse and around it.
Don't omit checking the wire connections to the battery either.
And to the back of the ignition switch.
Could be the switch itself too, we have seen before.
Have fun !

A bad battery will not instantaneously return to 13V after a load. It will take some time to recover. If you charge your battery and let it sit for a day or 2 and it still reads 12.7V it's probably good, but not always. If one of your rear lights works, check into the other circuit. An incandescent lamp will drop a bad battery voltage pretty quick. I'm still betting you have a high resistance connection somewhere. I really couldn't believe how bad my ignition switch was, it was like there was no battery there but I couldn't see it with a resistance check. Kill switches are the other big culprit. When I took apart my ignition switch to clean it, it looked fine, but worked fine after I cleaned it up. Remember, some of this stuff is 40 years old.

+1 to Rohan.

DogT said:

Kill switches are the other big culprit. When I took apart my ignition switch to clean it, it looked fine, but worked fine after I cleaned it up.

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Never thought about that! Will check that point too!

Remember, some of this stuff is 40 years old.

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Oh yeah... I know that!