12.5 V at Headlamp socket, no load, but only 11.5V with bulb connected

[mikepier]

Hello, lately been noticing my headlamps are not as bright as they once were. These are the original bulbs from 99, and the headlamps lens are in pretty good shape, they are not oxidized.

Just to confirm, I went to check the voltage at the socket with the lights on, and was getting 11.5V. Then I took out the bulb and was getting 12.5V, no load.

Is this normal? Or could it be my bulbs are so old it could be causing this drain of almost 1V?

I did not want to rush out and buy new bulbs if the voltage was the issue , and not the bulbs.

 

[1998Exp]

It has nothing to do with the bulbs; the voltage drop is along the wiring and/or switch contacts -- more likely the latter. Deteriorated socket contacts could also contribute to the problem. Poor ground connection is another source of drop (measure the voltage difference between the ground pin of the socket and the negative terminal of the battery with the bulb installed). Without the bulb there is no current, so no drop along the way, and you are measuring the battery voltage at the socket. When current flows, any resistance along the way contributes to the difference. 1V drop is probably within the manufacturer spec, but that doesn't mean that you have to live with it. Unless the issue is poor ground, you can purchase a harness with a built-in relay and a short, direct connection to the battery positive terminal, which will greatly improve the situation.
Sadly, the double filament 9007 bulbs and the Explorer reflectors are, in my opinion, one of the poorest headlight designs in recent history. One way to improve is to replace the OEM bulbs with a better performance 9007's. There is variety of those, and I can't recommend any, but by searching this forum you will find what worked for some members.

Hello, lately been noticing my headlamps are not as bright as they once were. These are the original bulbs from 99, and the headlamps lens are in pretty good shape, they are not oxidized.
Just to confirm, I went to check the voltage at the socket with the lights on, and was getting 11.5V. Then I took out the bulb and was getting 12.5V, no load.
Is this normal? Or could it be my bulbs are so old it could be causing this drain of almost 1V?
I did not want to rush out and buy new bulbs if the voltage was the issue , and not the bulbs.

 

[SoNic67]

That voltage drop is about normal. The wiring on cars is "economical" so some of the "improvements" that you can see on the net relates to providing bigger wiring for headlights. It's easier just to improve the ground wire, because the other "side" (positive) goes trough switches and relays.

Other option, cheaper, is to use a higher "efficiency" bulb. Those are made to run at 11.5V, so they will be brighter that a standard bulb. On the downside, they will last shorter time than the regular bulbs.
Look for something like GE Nighthawk PLATINUM or Philips X-tremeVision.

 

[Robman]

Maybe your battery is getting old? With the vehicle off, using the lights cause a decent drop in voltage especially with an aging battery.

With the vehicle running, this shouldn't be an issue as voltage would be bumped up to 14v or so making it just that little bit more efficient with some fresh amps.

If you wanted to get real fancy, I'm sure you could install a capacitor somewhere to help with the start up hit of high wattage stuff.

 

[J_C]

Turn the engine on then compare empty socket vs bulb lit voltage to determine if your battery is weak. There should be about the same 1V drop if the battery is okay. If that's the case then it's marginal wire gauge from the factory, possibly in conjunction with deteriorated contacts along the way.

With your multimeter still in voltage measurement mode you can measure the drop across various points in the system for example across a fuse, relay in/out contacts, fuse to bulb socket, relay to bulb socket, relay to fuse, bulb ground pin to battery ground terminal, etc. Unfortunately you're probably losing a little here and there instead of a single point issue.

It might even help to just take the fuse(s) and relay(s) out and push them back in and out a couple times to abrade away a bit of oxidation or grime.

I think Sonic has the right idea, that if you get those high brightness bulbs that *normally* have a much shorter lifespan, running at the lower voltage you should have a brightness increase over the stock bulbs but not so short a lifespan as would be seen if they were at closer to 14.0V in operation.

 

[toypaseo]

Look for something like GE Nighthawk PLATINUM or Philips X-tremeVision.

For some informative reading, look up online "Auto Express" and Philips X-treme Vision. The X-treme Power bulbs were past winners of their yearly headlight bulb tests. That is why I originally started looking at those, and bought them for both my Explorer and Paseo. The X-treme Vision bulbs were the 2014 winner, http://www.powerbulbs.com/us/blog/2014/05/philips-win-auto-express-headlamp-bulb-of-2014

 

[mikepier]

Turn the engine on then compare empty socket vs bulb lit voltage to determine if your battery is weak. There should be about the same 1V drop if the battery is okay. If that's the case then it's marginal wire gauge from the factory, possibly in conjunction with deteriorated contacts along the way.

The car was running when I took the measurements. The battery is approx 2 years old.

On a side note, I also measured the battery voltage while the car was running with no load, and it measured 13.7V. I thought it was on the low side. Is that within specs for the alternator output?

 

[SoNic67]

Oh, no, with car running and a good alternator you should have 14.2-14.5V...

This measurement should be done right after starting the engine. Some cheap alternators want to have minimum 1000rpm to work properly - that means that idling with those will not charge the battery correctly.
A 13.5V value also can mean that a diode inside the alternator is shorted, putting AC current in the battery and could even mess up with some sensors readings (like the Camshaft Position Sensor).

 

[J_C]

Oh, no, with car running and a good alternator you should have 14.2-14.5V...

This measurement should be done right after starting the engine. Some cheap alternators want to have minimum 1000rpm to work properly - that means that idling with those will not charge the battery correctly.
A 13.5V value also can mean that a diode inside the alternator is shorted, putting AC current in the battery and could even mess up with some sensors readings (like the Camshaft Position Sensor).

I agree that with that engine-running voltage the alternator could be bad, but that 1000 RPM to work properly isn't engine RPM, it's alternator RPM.

Alternator pulley ratio is probably at least 2.5X and should be capable of at least a few dozen amps at engine idle. Certainly enough to run the engine, lights, and (albeit slower) charge the battery.

Something else is strange though, if the battery measures 13.7V but the headlights are reading only 12.5V without the bulb, OR is that 12.5V without the bulb but the other bulb is still plugged in? With both bulbs out of the sockets, no load on that portion, it should measure the same as the battery voltage.

Some info is still missing like how long the vehicle had sat letting the battery drain then how long after it was started did it read the 13.7V? I could see possibly having a partially drained battery then starting it and not having it jump up to 14V at first, but it should get there within a few minutes.

If after the engine is off, the battery voltage drops down to about 11V or lower, I'd suspect a bad cell in the battery. If it doesn't drop that low then bad alternator.

 

[mikepier]

I agree that with that engine-running voltage the alternator could be bad, but that 1000 RPM to work properly isn't engine RPM, it's alternator RPM.

Alternator pulley ratio is probably at least 2.5X and should be capable of at least a few dozen amps at engine idle. Certainly enough to run the engine, lights, and (albeit slower) charge the battery.

Something else is strange though, if the battery measures 13.7V but the headlights are reading only 12.5V without the bulb, OR is that 12.5V without the bulb but the other bulb is still plugged in? With both bulbs out of the sockets, no load on that portion, it should measure the same as the battery voltage.

Some info is still missing like how long the vehicle had sat letting the battery drain then how long after it was started did it read the 13.7V? I could see possibly having a partially drained battery then starting it and not having it jump up to 14V at first, but it should get there within a few minutes.

If after the engine is off, the battery voltage drops down to about 11V or lower, I'd suspect a bad cell in the battery. If it doesn't drop that low then bad alternator.

Car not sitting, it's a daily driver.
Yes, 12.5 volts is with only one bulb out. Other bulb still in.
But in both cases (bulb out,bulb in) I get 13.7 volts at battery.
Never had issues starting before.

I measured battery voltages on other my other 2 cars when running, and got 14.1v and 14.2v., so not sure now if I do need to change alternator. The truck has been running fine.

 

[Robman]

Does your battery gauge in the truck sit right in the middle when it's running?

On an old explorer I used to get 13.7 and the gauge never really sat in the middle.

I put a new alternator in and it went to the middle ie: 14+ volts.

Chances are your alternator may be on it's way out.

 

[mikepier]

Does your battery gauge in the truck sit right in the middle when it's running?

On an old explorer I used to get 13.7 and the gauge never really sat in the middle.

I put a new alternator in and it went to the middle ie: 14+ volts.

Chances are your alternator may be on it's way out.

Its not in the middle, its a little below, but I never noticed any warning lights come on.

I also checked the voltage of the battery with the car off, and its 12.1V.

My other cars read similar, both fairly new, 2015's, so maybe its just a tired alternator.

 

[Robman]

A healthy 12v car battery should be between 12.6 and 12.8 volts fully charged with no draw.

A healthy alternator should be putting out 14+ volts.

The age of a battery doesn't always tell the tale, even if it's a newer battery if you draw it down to be dead often or if it was cheap or crappy to begin with it could get weak early.

Sounds like if you have the money, I'd replace the alternator and battery and call it a day.

Clean up all your connections, battery/starter/solenoid/fuse-relay box(whatever it's called) .. all the 4gauge wire stuff.

If you replace just the alternator and keep the weak battery, you'll be making the new alternator work harder than it has to and potentially shorten it's life alittle bit also a weak battery is hard on the starter.

My alternator that was reading 13.5-7 worked for quite awhile but the new alternator made the gauge sit in the middle and provided the proper power.

*edit
I'm no rocket scientist but here's what I would do as a test:

Start the truck, have all the lights/stereo off and test the voltage. - If 14-14.5v it should be good. The alternator can churn out what? .. 130amps?
So if you then turn the lights on with it running and see a large, sustained voltage drop than chances are you have a bad ground/connection.

Turn the truck off, leave lights(interior too)/stereo off.. wait an hour and test the battery.. If below 12.3-4... git a new one. Can always get a load tester to test batteries.

Or, take the battery out and charge it with a battery charger for 5-6 hours? @ 5 amps or so, disconnect the battery, let it sit for a few hours and again test to see if it's dropped to below 12.4 ish than it's weak. - load test would help, I got 1 for 20 bucks Canadian on sale @ TSC.

Check the fluid levels in your battery?

Explorer headlights suck.. I'm thankful I atleast have foglights to combine them with. The blower motor on full + headlights and foglights makes the gauge dip especially at idle on every explorer I've had.

 

[SoNic67]

The 13.5V "works", but kills the batteries faster.
Like I said one of the 6 diodes is bad and that sends spikes/pulses of current trough the battery that eventually kills it.

 

[1998Exp]

This has been a long thread, but my impression is that we still don't quite understand what the O/P measured and are offering advice based on what we imagined rather than what he meant. So here is what I got:

1) Your headlight output has recently decreased, so you decided to test things
2) You were running the engine at idle with the headlights turned on. The voltage across the battery was 13.7V.
3) With the engine still running and the lights still on you removed one of the bulbs and measured 12.5V across the pins at the socket.
4) When you re-installed the bulb (engine still running), the voltage at that socket dropped to 11.5V.

Yes/No? Please correct as needed.

 

[mikepier]

This has been a long thread, but my impression is that we still don't quite understand what the O/P measured and are offering advice based on what we imagined rather than what he meant. So here is what I got:

1) Your headlight output has recently decreased, so you decided to test things
2) You were running the engine at idle with the headlights turned on. The voltage across the battery was 13.7V.
3) With the engine still running and the lights still on you removed one of the bulbs and measured 12.5V across the pins at the socket.
4) When you re-installed the bulb (engine still running), the voltage at that socket dropped to 11.5V.

Yes/No? Please correct as needed.

Yes to all.

 

[1998Exp]

So now that I know what's going on, here is my 2 cents:

1) I don't think you have a bad alternator or a bad battery. To the best of my recollection, the manual does not specify the voltage at idle speed, and calls for loaded tests to be conducted at 2000 RPM. Even at that speed, the voltage has a wide range, and 13.7V sounds acceptable. It would certainly be more than enough if it appeared directly at the headlights...

2) You definitely have high resistance along the headlight circuit. One bulb drops 1.2V (13.7-12.5=1.2), two bulbs drop 2.2V (13.7-11.5=2.2). That works out to around 0.2 Ohm total (because the total headlight current is about 10A).

3) It is not very practical to put your finger on where exactly that high resistance occurs. I would check the following:
-- Corrosion on battery cables (including the negative one and under the insulation)
-- Corrosion on ground connections to both headlights

Clean/repair those as needed.
If that solves the problem (say reduce the drop with both bulbs from 2.2V to 1.0V), great, otherwise:

4) The positive connection to the battery is long and complicated (especially if you have auto-lamps). It is not practical to trace it, and parts may be too expensive to replace, even if you find the culprit. Instead, I would install something called Relay Headlight Harness (9007 version). These are made by many sources and provide a short, direct, and fairly heavy gauge connection to the battery, where the high current flows. It plugs into one of the bulb sockets and uses the voltage there only as a signal to operate a relay, so it doesn't matter how much resistance is in your original circuit (within reason, of course -- it still needs to draw 0.1A or so to operate its relay). Note that these usually do not provide a direct negative connection to the battery, and just hook to the body somewhere. These connections must be clean, tight, and corrosion resistant, and they still rely on good quality negative connection between the battery and the vehicle body.
If you go that route, check reviews before you spend your money - as with anything, some are junk and some are great.

Good Luck!

Yes to all.