1990 FLHTCU Drains Battery
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Stage II
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1990 FLHTCU Drains Battery
I have a 1990 FLHTCU with 55000 miles on it. It recently started to have an intermittent problem where it will drain the battery when the bike is parked and everything is turned off. I have checked the battery, charging system, draw when starter is engaged, and current draw when everything is off. The current draw when everything is off was in spec every time I checked it except one time when it was high. Since the problem only occurs once in a while I have been having trouble finding it. Anybody had a similar experience? Any idea's of where I should look to find the problem?
HDF Community Team
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From: NC USA
I'm assuming you have a volt gauge and keep an eye on that when riding and the system is charging correctly otherwise. From the positive to the regulator wire (disconnected), amp reading should be no more than 3 milliamps. It's important to check it that way, rather than simply at the battery post, so you can isolate the regulator draw from the other constants (memory/clock)
One that's too often overlooked... with regulator-to-battery wire connected, unplug the regulator from the stator at the engine case and check across the 2 pins of the regulator. If you have voltage there - bad diode in the regulator. They will often charge in that condition, but it acts like a tiny short that will leech a battery.
And keep in mind, radio memory and clock will run one down, especially an older battery if it's not started every 3-6 weeks. Again, depending upon the condition of the battery. Good luck.
One that's too often overlooked... with regulator-to-battery wire connected, unplug the regulator from the stator at the engine case and check across the 2 pins of the regulator. If you have voltage there - bad diode in the regulator. They will often charge in that condition, but it acts like a tiny short that will leech a battery.
And keep in mind, radio memory and clock will run one down, especially an older battery if it's not started every 3-6 weeks. Again, depending upon the condition of the battery. Good luck.
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Stage II
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Yes, I do check the volt gauge often and it is reading normal. I did the check across the regulator pins and got no voltage. I am not sure I understand the first check you mentioned from the postive to the regulator. Do I check current draw from the battery post to the regulator connections at the front engine case? Thanks for the help, I appreciate it.
HDF Community Team
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From: NC USA
My apologies, sometimes fingers don't say what brain is thinking. 
OK, if you have checked draw at the battery (from/between battery to main power cable) and it checked good, these may be redundant steps, but I'll give them to you anyway..
The battery cable will remain connected for all this.
Disconnect the lead from the regulator where it attaches to the main breaker. Check for current draw at (across) that point (between the lead and the breaker) - should be 3 milliamps or less. Oh, use test clips too. Your fingers/body will carry a measurable amount of amperage across a meter that sensitive. If that checks good, regulator is no longer suspect.
Then, disconnect the wire the that feeds the system, again at the main breaker, opposite of the battery voltage. Test between the breaker and the lead for the system. Should read about 15 milliamps or a touch less.
If all that checks out, I'd guess a cell in the battery is weak and leaching the others.
OK, if you have checked draw at the battery (from/between battery to main power cable) and it checked good, these may be redundant steps, but I'll give them to you anyway..
The battery cable will remain connected for all this.
Disconnect the lead from the regulator where it attaches to the main breaker. Check for current draw at (across) that point (between the lead and the breaker) - should be 3 milliamps or less. Oh, use test clips too. Your fingers/body will carry a measurable amount of amperage across a meter that sensitive. If that checks good, regulator is no longer suspect.
Then, disconnect the wire the that feeds the system, again at the main breaker, opposite of the battery voltage. Test between the breaker and the lead for the system. Should read about 15 milliamps or a touch less.
If all that checks out, I'd guess a cell in the battery is weak and leaching the others.
Last edited by t150vej; Jul 21, 2009 at 08:56 AM. Reason: corrected info
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