2007 Honda Fit with headlight/power problem

Hey guys and gals,
I recently purchased a 2007 Honda Fit and everything is good except for one thing. The headlights, interior dome light, and one light on the climate control dashboard pulse when the engine is on. The brightness pulses to be exact, and it becomes more intense at higher speeds, and when the car is in gear and not in neutral (this is a manual stick). It is not noticeable during the day, but a pain at night.

I took it in to get looked at and two different mechanics (including a Honda dealership) said they cannot figure out what is wrong with it. They tested the battery, alternator and voltage regulator, and they all tested fine. The guy at the Honda dealership played with the wire to the battery and it got a little bit better. They said replacing the alternator (which seems to be fine) is the only fix they can think of ($650).

If anyone has the same problem out there, or any suggestions, I am open to everything.

Thanks for the help!


“I took it in to get looked at and two different mechanics (including a Honda dealership) said they cannot figure out what is wrong with it.”

“(including a Honda dealership)”

In my frustration, I would not be able to resist the urge to call Honda Corporate and ask if they knew of any place they could recommend to get one of their cars diagnosed and repaired.

If you try that then please let us know where it takes you.


It could be many things, like bad grounding, alternator, regulator, battery, etc - one would hope they checked all those things. A bad ground strap to a particular part of the chassis could easily do that, for instance.

Do you know if they checked your ELD (Electric Load Detector). It is supposed to adjust the voltage output off your alternator under varying loads. If that thing is misbehaving, it can vary the voltage at random.
It is usually located in the fuse box under the hood.

Agreed with all of the above…

The battery might test OK, but it still could be the battery. At night all the lights are on and if the battery is taking too much current off the alternator to recharge you might see more dimming of the lights. Replace the battery with the highest quality one you can get to fit the size.

Another thing you can try is to put the current battery on a charger (battery tender) type overnight. This will make sure the battery is up to a full charge. If your driving pattern is a lot of city stop and go, short times, and lots of motor restarts as you shop and do errands; all this can lead to only a semi-charged battery. A good road trip of 100 miles now and again is good for the battery and if this is a rare event in the life of your car the battery could be working at 1/2 charge much of the time.

Hey everyone, thanks for the help. I picked the car up from the Honda dealer today and he described what he checked. It included checking and cleaning the grounds, testing the output on the battery and alternator, and tightening up a cable that was loose on the battery. They also accidently left the dome light on so when i went to get the car in the parking lot the battery was dead. After a quick jump I was off driving the car home and so far, the brightness pulse of the headlights has gotten much better to the point where it is hard to notice. So although they didn’t know what was wrong, something they did while tinkering with it helped out. I’m thinking either cleaning and getting a better battery connection or maybe ‘resetting’ the battery by letting the charge run down on accident. Either way, all is well for now. I will send updates if anything changes.

Thanks again for the help!

So more updates, the brightness pulsing is back the next day after i picked it up and recharged my battery ( because they killed the battery with the dome light - see thread above). This makes me think that the reason it was running better was that the battery had a full charge and that somehow my alternator is not fully charging it. Im going to test this theory by charging it up again and seeing if it goes away.

The other possibility is the battery is just bad and cant recharge, and needs to be replaced.

Any other thoughts from anyone?


I would be very surprised if this did not turn out to be a case of a failing alternator.

The pulsing headlights used to be a classic symptom of a bad voltage regulator overcharging the battery. Letting the battery run down would temporarily " fix" the problem until the battery reached a full charge and beyond. I think your battery is overcharging, if you have removable caps you can look in when the lights are pulsing you should see a lot of bubbles coming up if it is indeed overcharging.
Unfortunately, I don’t know what to do about it on a modern car, I have been told that the computer controls charging rates but I don’t know if it is true.