66 TBird Headlights Kill Battery | Ford Thunderbird forum club group 1955-2005 models

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66 TBird Headlights Kill Battery

pafudd

pafudd

Bronze Member
Reaction score
1
Thunderbird Year
1966
We have chronic issue with charging system. Headlights will eventually kill the battery if we our out for an evening drive. Didn’t last 15 minutes the other night. Stopped for an ice cream and car wouldn’t start. Got a boost and drove home. Tinkered with it in driveway next day. Battery voltage is stable when idling and lights off. Voltage drops below 11 volts in less than 15 minutes idling with headlights on. Alternator was replaced several years ago with 65 amp Wilson. Battery is 12 years old but we use a battery tender over the winter. We put on about 100 miles/year. Need some coaching on troubleshooting. Thanks.

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From what you said, when idling and the lights are on your voltage drops suggests the alternator isn't charging. Usually, when running I'd expect the voltage to increase not decrease almost taking the pressure off the battery maintaining the power. If the battery was an issue, whilst running shouldn't make much difference until you stopped and tried to start or from cold as the battery provides that power needed to start before the alternator kicks in. Does that make sense?
 
Bad Battery. Don't waste your time denying its the issue. After changing it use a voltmeter to check alt output at idle.
 
Critterpainer said:
Bad Battery. Don't waste your time denying its the issue. After changing it use a voltmeter to check alt output at idle.
Click to expand...
Yes, agreed, and while you're at it, consider replacing the battery cables. They degrade over time due to water intrusion and overloading, and the contact points become gunky/corroded, which reduces power to the engine and starter. You could well have the original cables on that car. Inexpensive to do, cables are <$40 from Rock Auto.
 
I don't disagree about replacing the battery and all the cables, 12 years is a long time for an automotive battery. It could be the alternator also. I would check it by starting the engine and then disconnecting the + battery cable. If the engine dies its the alternator, if it keeps running the alternator is good enough to keep the ignition running. This test is what I would do.. perform at your own risk. 1 wire replacement alternators are not that expensive, even for a 100 amp. It's what I run on my 1964 with no problems. You might try driving it a little more. 100 miles a year barely keeps everything adequately lubricated. I put over 5000 on mine over the last year..I just love to drive it.
Take care
Ed
 
I know many people say to pull the battery cable while its running to see if the alt is working. Often the test works. Sometimes you get to open your wallet after frying the voltage regulator or if you have upgraded to electronic ignition, it too may get fried. A cheap voltmeter is $5.00 at Harbor Freight and sometimes free. Lots cheaper than whatever fried.
 
Critterpainer said:
I know many people say to pull the battery cable while its running to see if the alt is working. Often the test works. Sometimes you get to open your wallet after frying the voltage regulator or if you have upgraded to electronic ignition, it too may get fried. A cheap voltmeter is $5.00 at Harbor Freight and sometimes free. Lots cheaper than whatever fried.
Click to expand...


I knew I would be criticized for mentioning that test. Exactly why I put the caveat in my post.. No one asked if the Ampere gauge is working? If it is that would help in determining if the alternator is charging. If when you turn on the headlights and the amp gauge goes to the left side of the center of the gauge then the alt is not supplying enough current to run the headlights. I hope you determine the problem and get it resolved. I guess you could just drive it to Autozone where they will test the battery and the alternator for free.. easy peasy..
Take care
Ed
 
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Glad we joined this forum and appreciate all input. Battery replacement was already in the cards. Just wanted to be thorough. Also replacing original headlight switch to deal with periodic loss of lights and going to check headlight grounds to troubleshoot dim headlights... BTW.. we live in Alberta so our Bird goes into hibernation soon and wakes up late April
 
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