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Discussion Starter · #1 ·
I have a 71 T120 and I have always had an issue with leaving the battery hooked up for long periods of downtime. However, now i can not leave the battery in overnight without it draining to the point of not being able to start it. The alternator is fine, I am getting normal amps when in idle. I have the original Zener Diode, which I hear are terrible, could that be where my problem is? I have no idea what could be drawing the current? Any ideas?
 

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pull the wire off the zenner when you park it next - not a perfect test - but if it doesnt drain down then it may be the zenner - -- if there is no change in the discharge I would then disconnect the wiring to the rectifier and see if it drains - always one thing at a time -- lots of other possibilities but start with the easy tests first
 

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have a 71 T120 and I have always had an issue with leaving the battery hooked up for long periods of downtime.
OK without a supplemental charge over a period of time a battery will loose its charge, begin to sulphate and eventually kill it. This is normal.

However, now i can not leave the battery in overnight without it draining to the point of not being able to start it.
A near dead battery will take on what is referred to as a "surface charge" when charged, but will quickly (overnight) loose it.
Simple test — remove the fuse when you put the bike up for the day.

I have no idea what could be drawing the current? Any ideas?
A battery that has gone high resistance from sulfation???
 

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Discussion Starter · #5 ·
Thanks for all the replies. I'm not great with the electrical and didn't think I would be able to disconnect the zenner and rectifier to test it, but after thinking about it you are right. So currently i have the zenner disconnected and we shall see how it goes. It can really only be the power switch, the zenner, or the rectifier so i should be able to figure it out pretty quickly hopefully.

As for the multimeter i can try that but I'm not sure how to search for a drain on the rectifier. Also would it even pop up on a meter?

And as for the battery, it is fresh and I know that it is not the battery, it holds a charge when not hooked up the bike. I usually avoid this problem by just keeping it disconnected.
 

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How do you check for a drain with a multi meter. Guessing here, multi meter set to ohms, putting a probe on a wire or device with the other probe to ground and checking for continuity.
 

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How do you check for a drain with a multi meter. Guessing here, multi meter set to ohms, putting a probe on a wire or device with the other probe to ground and checking for continuity.
Multimeter set to mA (milliamp current). Remove the lead from the live battery terminal, connect meter lead black to battery, red to loose lead (if positive earth).

So the meter is in series, as part of the circuit that you suspect is passing current. The meter should show zero mA.

If it shows a definite reading, try disconnecting a likely suspect, such as Zener to earth connection, or rectifier to earth, or rectifier to alternator.
 
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