Hello, I have a 1966 coupe with 289 4speed. When I turn on the headlights the volt meter drops to about 10 and as soon as I turn it off it jumps back up to 13. Just had the alternator rebuilt and still the same issue. I am running a normal cd player with no amp or extras. Wondering if there is a test I could do on the lights to try and track down the problem. Anyone have any ideas or similar problems??? thanks.
battery drains with headlights on????
- Thread starter riddler1
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2nd Mustang
Founding Member
External regulator and has that been changed? What kind of headlights? What happens when you increase the rpms after turning on the headlights?
Tim65GT
Active Member
What type of gage do you have? Where is it tied into? Are you measuring the same with a external handheld voltmeter? Does it actually kill the battery or are you just going by the gage indication?
Last summer I was driving it and with the lights on, the aftermarket volt meter was reading low about 10, when i turned the car off the battery was dead when i tried to restart. As soon as the lights get turned offf the voltmeter jumps to 13, not sure where it is tied into as of yet as the car is in a garage as it has snowed here again!!!!!!! Will check when I get into it again. Over the winter I rebuilt the alternator as I guess it was suspect......battery seems to charge fine but early this year I tried the lights with the rebuilt alternator and the volt gauge dropped again. Battery seems to be good as it takes a charge with the lights off and seems fine, just when I use the lights. anyways......
Tim65GT
Active Member
When you get a chance, have someone turn on other accessories while you check the voltage at the battery with an external voltmeter.
As they turn on the wipers, apply the brakes, heater fan and then turn on the lights, see what each item does individually and separate to the voltage.
If it is in fact only your lights that cause the voltage to dip, pull the headlights and re-check to see if it still does it.
If something was mis-wired and it causes the voltage to dip that far, I would think there would be a wire melting somewhere.
As they turn on the wipers, apply the brakes, heater fan and then turn on the lights, see what each item does individually and separate to the voltage.
If it is in fact only your lights that cause the voltage to dip, pull the headlights and re-check to see if it still does it.
If something was mis-wired and it causes the voltage to dip that far, I would think there would be a wire melting somewhere.
2nd Mustang
Founding Member
Really, try increasing the rpms when the headlights are on. If the voltage increases to 14, I would suspect the voltage regulator. If at idle it reads 14 volts and you turn on the headlights and it drops to below 13 volts, I would suspect the regulator as you mentioned that the alternator checks out good.
Good luck.
Good luck.
well new update on the lights, drove the car last night and when I put the lights on the volt meter shot up to 16 and stayed there for the time I was driving the car, probably about 5 min. I turned the lights off and the meter went back to 14 and with them back on, shot right up to 16. Could this possible be the regulator, with changing the rpms didn't seem to affect it and it just stayed at 16. hmmmmm.
2nd Mustang
Founding Member
Sixteen volts does seem high. Sounds like it's overcharging which isn't good either.
At idle with the headlights on, the voltmeter should dip initially below 14 volts, but then go back to around 14 volts.
At idle with the headlights on, the voltmeter should dip initially below 14 volts, but then go back to around 14 volts.
just like to say thanks for all your help, turns out it was the voltage regulator, as soon as I changed it out the volt stays rock steady at little over 13 volts. Haven't tried running for a while with the lights on but am expecting good things, thanks for all your input, this site is alot of help.
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