Searching an electrical problem

[andyvh1959]

It can seem daunting to find out why your bike keeps draining the battery, especially if it had not done it before. A lot of people assume "time for a new battery", spend the $100 and the bike is good for a while, maybe even a season. Yet, the next spring the battery seems to be the issue again, when it likely is not the real issue. But a methodical approach to it, some patience, and a volt/ohmeter can tell you a lot.

Get access to your bike battery. Remove any body panels, fuel tank, headlight, so you have access to all connections. Best if the battery is fully charged, which you can confirm by checking the DC voltage across the terminals. But what you really need to check is any amperage load in the system that is draining the battery down over time. Set your voltmeter to the highest range for Amps to start with. Disconnect the positive at the battery and connect the meter INLINE between the battery positive and the positive cable you just disconnected from the battery. Make sure none of these connections can touch any metal on the bike.

If all is well with your bike the AMPS setting should be zero, meaning no drain on the system. But, you need to step down the meter AMP range to check if a mili-Amps draw is draining the battery. Anything more than about 2 mili-amp is enough to drain the battery down over time. If the amp reading is say 10 mili-amp you need to find where it the potential issue is. With the meter inline to the positive, go through the entire bike disconnecting one line at a time. When you locate the circuit, the meter will show Zero amps when you disconnect it. That at least directs you to which circuit is causing the issue.

For example. I installed a stereo into the fairing on my buddy's VN900 by tapping into the front accessory plugs in the wiring harness. But over time it would drain the battery because the connections went to the battery and not switched power through the ignition. So I installed a relay in the circuit, and the relay is controlled by the ignition. Key off and no power to the fairing. Now, I know the issue is the way I had installed the power to the fairing and stereo. But say I had bought the bike the way it is and didn't know how the fairing/stereo had been wired. By doing the Amps draw test at the battery when I disconnected the fairing power connection the meter would go to zero, so from that I'd know what circuit to check, or install a relay.

[JD Hog]

Great information!

[andyvh1959]

Forgot to add, and this should be common sense, but it can happen. With your voltmeter set to AMPS and with the voltmeter installed inline between the battery positive post and the positive cable, DO NOT attempt to start the bike! It will at minimum quickly fry the voltmeter leads, and likely fry your voltmeter.

[The Black Knight]

Thx mate.