Both headlights burned out tonight... Why?

[Green Monster]

It's dusk and I come out of a store about 15 minutes from home. I hop in my 72 Blazer and start driving down the road. About 2 minutes into the drive toward home I see a flash in that projected to the front of my Blazer from what I thought was behind me.

My wife asked, "What was that?"

I replied, "You saw that too? Must have been a strobe light from some ricer or strobe in a red light that we just drove under."

One minute later, another flash, but this time it is evident that it came from the front of my Blazer as the car in front of me moved from the left lane to the right lane in a hurry. Now I'm driving in darkness and can tell my headlights are gonzo. I hit the high beams switch on the floor and both lights flash and burn out immediately. Now I'm in total darkness. I pull over and check the parking lights. I have all parking lights and signals work fine. Interior and dash lights work too. Its getting dark in a hurry as the sun has already set. So I drive home with the parking lights on and follow any car I can get behind just so I can see where I'm going.

So, what happened there? The headlight switch was not warm, nor have I ever encountered it being warm. I have not messed anything electrical on this truck. I have owned it since 2003 and installed Sylvania SilverStar headlights in spring of 2004 without any issues since. I have never had both headlights blow at the same time, high beams too on any car I have owned.

Sound like a short or bad ground? I figure my fuse would have gone first. I don't know for sure though. What should I look for.

[1971K54X4]

May be just bad luck?

[Green Monster]

I could understand the low beams, but the high beams too. Something is wrong. I love the SilverStars and really don't want to spend money on another set only to burn them up as soon as pull the headlight switch. I suppose I could connect my volt meter... but how many volts or amps should I look for?

[1971K54X4]

Same as what you have across the battery.

[Green Monster]

So the juice should match the battery. So what would cause the issue, too high or too low volts/amps? Or am I looking for the wrong things?

[jrb71c20]

I blew both mine out last year leaving the parking lot at work (2nd shift). The both lit up bright and blew out. Turned out to be my voltage regulator, Im still running an external. I had to replace my dimmer switch too.

[jhow66]

Headlights are not fused. They are protected by a circuit breaker that is made into your light switch so that the lights will just flash on and off if there is a short in the feed wires. Your problem is the dimmer switch. Unplug it(with lights on) and use a jumper wire from the blue wire to the green wire. High beam should come on. Now jump from the blue to tan-low beam should burn. If this works , change dinmmer switch. If not, take a test light and unplug a headlight. Have someone to do the jumper deal while you check to see if you are getting power to the lights (this will save you from buying new lights if you don't need them. If no power to headlights, change light switch.(There should power to light switch at all times on the red wire) If this does not work for you, let me know.

[69TowRig]

Originally Posted by jrb71c20

I blew both mine out last year leaving the parking lot at work (2nd shift). The both lit up bright and blew out. Turned out to be my voltage regulator, Im still running an external. I had to replace my dimmer switch too.

I'm with him, check the voltage regulator, sounds like an overvoltage.

[old man jimmy]

I'll go along with 69 tow rig on the voltage regulator. But if you got that kind of a spike it's funny you didn't loose more bulbs. Not familier with the lights you were using, but could be they are pretty much running at the max for ultimate brightness, which may have put them first on the list to blow. Sorry jrb, I agree with you also.

[Green Monster]

I appreciate the comments from all of you. Now I have an idea of what to do to remedy this problem.

jrhow: Thanks for the testing instructions. You indicated that my problem is my dimmer switch. You also indicated if test results may warrant the replacement of the headlight switch. I'm under the impression these switches the same switch. Or are they two different switches?

These lights lit up like a strobe. I'm 99% positive they are gone. On a side note: I have had circuit breaker issues on my 88 Mustang where the lights turn on and off due to an overload. This was a result of the factory wiring being in insufficient for the factory fog lights. Heat buildup caused the breaker to trip off and on. I added a relay and and direct power from the battery to the fog light which was a remedy that issue. Has worked great for years now.

A faulty voltage regulator seems to make sense as suggested by jrb, 69towrig, and old man jimmy. The rest of my lights did appear bright, but did not burn out. I could not determine if the lights were actually brighter or if my pupils were dilated from driving home without headlights.


Where is the voltage regulator located?
Is a voltage regulator something a local auto parts store would carry?

[pound41]

Dimmer Switch is the push button in the floor for the headlight. head Light switch dimmer for running lights

[Green Monster]

Update:

I parked the Blazer last night. Came out this morning to check the voltage at the battery and at the headlights. 8.00V at the headlights and 8.15V at the battery. I turned the key to start the motor and nothing. No click. No crank. Nothing. The parking lights work and the under dash lights work. The radio does not work. The radio is an after market radio that is apparently tied into the red wire coming out of the back of the ignition switch at the dash. The ignition switch is original. I'm inclined to think my ignition switch is bad.

Is the bad ignition switch what caused my headlights to blow? Or is this just one over several things that has failed as a result of another problem, like a faulty voltage regulator?

[Yukon Jack]

The external voltage regulator is bolted to your radiator core support on the driver's side. Sounds like a good time to look into changing to an internally regulated alternator if the external regulator is causing your problem.

Are your present headlights a big power upgrade over the standard headlights? If so, maybe you should also look into rewiring them using relays to get more power to them.

Good luck finding the problem - I know how much I hate dealing with electrical gremlins!!!!

[Yukon Jack]

BTW, I'd recommend posting this in the Electrical section too - there are some real knowledgable members in that forum that might be able to help.

[1971K54X4]

you need at least 12 volts at the battery. I would look at that as to why it would not start. In my opinion this looks like an alternator problem.

[jhow66]

"jrhow: Thanks for the testing instructions. You indicated that my problem is my dimmer switch. You also indicated if test results may warrant the replacement of the headlight switch. I'm under the impression these switches the same switch. Or are they two different switches? "
Dimmer switch is the one on floor for high or low beam. The one on headlight switch is for dimming the dash gauge lights.

[Green Monster]

I posted this problem in the electrical section... I will take a look at my voltage regulator when I have some time on Monday. As of now, this appears to be the culprit.

Thanks guys.

Link

[LUV2XCLR8]

Hope that fix's it, stuff like this will drive you

[old man jimmy]

I'd check your battery also. If your's is about 3 or 4 years old, and not a lot of life left in it. Sometimes an overcharge is enough to push it over the edge. For your ignition switch. I don't see anything in your posts that leads me to believe there's anything wrong with it. Try charging your battery and see if it will hold. If not, charge it with cable off, and see if it will hold a charge that way. If not, time to get a new battery. What I mean is let it set overnight, and see if it's still holding a little over 13 volts.

[gringoloco]

Old man jimmy has it right. Your voltage regulator is shot causing an over voltage which leads to blown headlights and fried batteries. Jump the truck off and check the alternator output- betcha it's around 17V or higher. Replace it with an internally regulated style as suggested and get new headlights. Hope your battery isn't smoked and will take a charge, but the prognosis for it is not good...

[Green Monster]

I have the battery on a 2 amp charge with the cables off. It's taking about 1 amp. We'll see where I'm at tomorrow. Why the urge to purchase an alternator with an internal volt regulator? Are the external volt regulators that bad? I would rather keep the Blazer as close to stock as possible.

Thanks for the help.

[Long Roof]

I think people have found them to be more reliable and cheaper.

[old man jimmy]

If your charger will go higher than 2 amp. Like at least 10. Would be a lot faster. It's going to take awhile at 1 amp to put a charge back in a dead battery. If your charger will go higher, I'd step it up to at least 10. Most will cut back as the battery starts to charge. How old is the battery. I have 6 old beasts, and batteries are a constant battle. Most get used very little. As for your alternator. I see nothing wrong with the old external regulator, I have 5 of them and one internal. I agree the internals are more relable, but the externals are cheap (around $12 - $15) and very easy to replace. And I have some of the regulators that are 43 years old & still fine. So they are not that unreliable. It's your truck, and unless you're just putting it together to sell. Make it the way you want it.. Have fun with it..
Tom

[jaros44sr]

10 amps aleast, I use 2 amps just to keep a battery topped off.... J

[Green Monster]

Okay... so I charged at 2 amps overnight on Monday night. I checked the Tuesday morning and the battery was still taking 1 amp. So I pulled the plug on the charger. I put the battery on a 6 amp charge tonight and it is taking 4 amps. I will check it out tomorrow morning. I disconnected the positive wire from the battery during charge because I don't really understand how I lost the charge in the battery to begin with. I'm afraid I may have a short somewhere. I would hate for my house to burn down because of a wiring issue in my beloved Blazer.

The wires look good. I checked them over. I will investigate further when I have more time. Probably Friday.

I'm just curious why my battery was drained. Yes it is a about 4 years old, but typically they die slowly, not just overnight... right?