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You need to test it running Posted by Ari [Email] ![]() ![]() In Reply to: Is My Headlight Voltage Too Low?, Aom, Wed, 19 Apr 2006 21:01:57 Members do not see ads below this line. - Help Keep This Site Online - Signup |
With the car off and the headlights on, I'll bet your battery voltage is a lot less than 12.7. I'll bet the battery voltage under load (lights on) and engine off is no better than high 11 volt range. And since you don't drive much with the headlights on but the engine off, the test is pretty meaningless.
What you can control, up to a point, would be any voltage drops on the way to and from the headlights. So with the engine running, measure the voltage between the positive battery post and the high side (12 volt side) of the individual headlights. The voltage difference should be less than about 0.2 to 0.3 volts. If it is any larger, you might look into cleaning any contacts, including the headlight relay contacts.
ALSO - measure the voltage between the LOW side of the headlights and the battery negative post. That should be a very low voltage difference - less than about 0.05 volts or so, since all the conductors are good. A poor ground is as bad as a voltage drop on the high side.
Assuming all is in line, then yes, the headlights are what the headlights are.
Why do the test with the engine running? That's because the voltage will be a little higher. Voltage drops will be slightly different. Enough to matter? Yes. Even a few hundred millivolts of voltage drop will create a visible difference in headlight output.
Lastly, how old are the bulbs? Halogen bulbs, like many others, degrade over time. Old bulbs are dimmer than fresh ones.
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