Electrical Problem -Harness Drawing 2 Amps

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Hi there,
We got the electrical on the '72 interstate pretty much completed but have found one snag. We used a battery charger to test all the lighting circuits and everything worked good. Then hooked it up to the battery leads from the harness. With the key switched off, the charger shows a draw of 2 amps, which does not seem right. Is there anything you can think of as to why this draw of 2 amps is happening. We thought it might have something to do with the capacitor, but i really don't know much about electrical components so I'm a bit lost. Any help is appreciated.

Thanks,
Matt
 
mattthomas4444 said:
Hi there,
We got the electrical on the '72 interstate pretty much completed but have found one snag. We used a battery charger to test all the lighting circuits and everything worked good. Then hooked it up to the battery leads from the harness. With the key switched off, the charger shows a draw of 2 amps, which does not seem right. Is there anything you can think of as to why this draw of 2 amps is happening. We thought it might have something to do with the capacitor, but i really don't know much about electrical components so I'm a bit lost. Any help is appreciated.

Thanks,
Matt

Disconnect the capacitor and check again?
 
Use a battery installed, and a DMM in line with one battery lead, re-test, report back.
 
mattthomas4444 said:
With the key switched off, the charger shows a draw of 2 amps, which does not seem right. Is there anything you can think of as to why this draw of 2 amps is happening.

Try disconnecting the Zener diode.

But note that if it is the Zener causing the amp draw, then it's probably working normally.
 
Well, with the ign key in the OFF (not PARK) position, there should be absolutely NO current draw from the battery. None, zero,zip, nada! :)

2 Amps is a substantial draw so something is clearly faulty. Could be anything from a chafed wire/incorrect connection to a bad ignition switch. As suggested, the usual troubleshooting method is to disconnect components until the current draw disappears. From the post it sounds as if you have just recently re-done the wiring. I suggest you get out the wiring diagram and carefully go through everything again. With the ignition switch in the off position, no current should be flowing anywhere. If it is, something is miswired/shorted or the switch is bad.
 
mike996 said:
Well, with the ign key in the OFF (not PARK) position, there should be absolutely NO current draw from the battery. None, zero,zip, nada!

Matt said he used a battery charger to test the circuits, not a battery, therefore the voltage from the charger could be high enough for the Zener to become conductive.
 
You are right - I failed to note that a battery charger was used, not a battery.

Put the battery in there in then test for any current drain with the switch off.
 
L.A.B. said:
mattthomas4444 said:
With the key switched off, the charger shows a draw of 2 amps, which does not seem right. Is there anything you can think of as to why this draw of 2 amps is happening.

Try disconnecting the Zener diode.

But note that if it is the Zener causing the amp draw, then it's probably working normally.

+1

If you have connected a battery charger across the battery(not fitted?) connections, then it is going to be outputting well in excess of 12V, probably close to 15v. At that voltage the Zener will be conducting a couple of amps to earth. As stated by others you need to fit the battery, and if you want to check any current draw, fit an ammeter in series with it.
 
Thanks for all the help, it was the zener diode. The battery also is supplying 17 V, that seems a bit high, is that abnormal, I'd think it should be around 14 V max.

Now if only the headlight switch would stay on, the switch on the handlebar must be broken or worn so a new one is on the way. I didn't notice anything when i took it apart though. Apparently it was the same way 35 years ago when the bike was still in use, my dad had to tape the button down so that the headlight stayed on.

Matt
 
mattthomas4444 said:
Thanks for all the help, it was the zener diode. The battery also is supplying 17 V, that seems a bit high, is that abnormal, I'd think it should be around 14 V max.

Now if only the headlight switch would stay on, the switch on the handlebar must be broken or worn so a new one is on the way. I didn't notice anything when i took it apart though. Apparently it was the same way 35 years ago when the bike was still in use, my dad had to tape the button down so that the headlight stayed on.

Matt

What are you using to measure voltage? What type of battery is it?
 
L.A.B. said:
mattthomas4444 said:
The battery also is supplying 17 V, that seems a bit high, is that abnormal,

Yes, that's too high,

Correct batter voltage is 14.3 to 14.7 volts as is the generator output.
It might be that you have a meter giving a false reading of 17 volts, if not this is too high a voltage and might be the cause of the breakdown of the Zener diode, and might break the new one.
I am no electrical expert but your electrics leave me deeply suspicious about your voltmeter.
 
Bernhard said:
Correct batter voltage is 14.3 to 14.7 volts as is the generator output.

The charging voltage may be as high as that, but the static voltage of a charged 12V battery would normally be lower.


Bernhard said:
It might be that you have a meter giving a false reading of 17 volts, if not this is too high a voltage and might be the cause of the breakdown of the Zener diode, and might break the new one.

As the system voltage rises, the Zener becomes increasingly conductive because it starts doing what it's designed to do = regulate the voltage, this is nothing to to with it breaking down.
If you go back to the first post, it was mentioned that the amp drain occurred when a battery charger was being used to test the circuits (without a battery connected) the increased level of voltage from the charger can trigger the Zener.
 
i have a side question here this made me think of, normally with a car that has a negative ground, i would test for a drain with a meter in series on the negative cable and battery. would it be opposite with the commando's because they're + ground?
 
kevbo82 said:
i have a side question here this made me think of, normally with a car that has a negative ground, i would test for a drain with a meter in series on the negative cable and battery. would it be opposite with the commando's because they're + ground?

It would be the same using the positive lead but the current would flow in the opposite direction.

Ian
 
kevbo82 said:
i have a side question here this made me think of, normally with a car that has a negative ground, i would test for a drain with a meter in series on the negative cable and battery. would it be opposite with the commando's because they're + ground?




The basic difference of positive earth/ground when compared with negative ground is that the current simply flows in the opposite direction around the circuit, but this does not mean you need to approach it any differently than you would negative ground-only ensure that polarity sensitive items such as electronic components or ignition coils are connected in accordance with the polarity.
 
But don't get confused - the fact the the current flows in the opposite direction has no bearing on any measurements you will make - whether you break the + or - side to get an amp reading makes no difference; the amp reading will be the same. Same is true of voltage - Yes, if you connect the the red multimeter lead to the neg terminal/black lead to the pos terminal you will get a minus voltage reading. But for normal system troubleshooting it is of no consequence - the voltage reading will be exactly the same either way. Whether there is a minus sign in front of it or not doesn't matter.
 
A lot of these questions would be answered by simply reading the Electrical section of the Workshop manual (Section J). :roll:
 
Old Bloke said:
A lot of these questions would be answered by simply reading the Electrical section of the Workshop manual (Section J). :roll:

Pretty sure it doesn't cover Negative Ground. Or testing while hooked up to a battery tender.
 
swooshdave said:
Old Bloke said:
A lot of these questions would be answered by simply reading the Electrical section of the Workshop manual (Section J). :roll:

Pretty sure it doesn't cover Negative Ground. Or testing while hooked up to a battery tender.

You'd be correct there. The OP's bike is positive ground, so the Workshop manual applies. Testing while hooked up to a battery tender wouldn't be covered because it's not the correct way to test or faultfind the power/charging system.

I'm not being pedantic. Norton done a lot of things wrong, but I always found the Electrical section of the manual to be fairly helpful.
 
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