Left brake light problem -- 2004 Santa Fe

I have a 2004 Hyundai Santa Fe V-6 with a 3.5L engine.
People keep telling me that my left brake light does not light up when I step on the brake. The right brake light works as it should.
It seems to be an intermittent problem. Sometimes, when people say the left brake light is not working, I back up to a store front window and step on the brake and the brake light on both sides are working.
Another time, I found that the left brake light was not working so I changed the bulb. The old bulb didn't necessarily look like it was bad, but I changed it anyway, and both brake lights then worked.
Shortly after that, I got stopped by a cop for the same thing (no ticket, he just let me know it wasn't working) and I changed the bulb again and both brake lights worked. The old bulb looked fine, but I changed it anyway and the problem went away.
Then, soon thereafter, once again someone told me the left brake light wasn't working, and I checked and it was not working. This time, I looked at the bulb again and it looked fine like before. So, I just cleaned the terminals on the bulb and socket and put it back together. That didn't fix anything, so the left side brake light is still not working once again.
Tomorrow, I am going to take both sides apart, then switch bulbs between the right side and left side and test it again. My guess is that won't fix the problem since I assume both bulbs are good.
I assume that there must be a loose connection or wire someplace, but I don't know how to check for that. I was planning on buying a test light anyway since I am also having an electrical problem involving the rear lights on an old bomb 1989 GMC pickup truck that I own. I am wondering if I could use the test light to try to narrow down the source of the Hyundai left brake light problem, but I don't know what or where to test.
Can anyone suggest anything else that I could try?
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On 12/20/2015 7:12 PM, TomR wrote:

Intermittent problems are a PITA. I'd start with the socket itself. Make sure the bulb is making proper contact and the socket is grounded. I have no idea were to trace the wire back to check each connection.
Alternative is to trade it in for an Equus.
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In typed:

Thanks. I decided that just buying Equus would be easier, so I did that.
Not really, of course, (unfortunately), but thanks for the other suggestions.
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TomR wrote:

I would get out the multimeter / ohmmeter and check the socket ground. You can check the bulb with the ohmmeter, too. No need to keep replacing them. No need for a test light either, use the volt function on the multimeter.
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In typed:

Thanks, but I am not sure if I would know how or where to check for the socket ground other than maybe getting under the vehicle and looking to see if there are any wires coming from the light harness that are grounded to the frame and check those connections.
I didn't try that yet, but I seemed to have already fixed the problem last night. Here's what happened when I did the fix last night:
I backed my car up toward the store window of a Pep Boys auto store, and I could look into the reflection in the store window and see that the left brake light wasn't working. Then I took off both back lens covers and removed the brake light socket from both sides (leaving the bulbs in the socket) and checked again -- same thing. I looked at the left brake light bulb and it looked fine. When I went to look at the right brake light bulb, that side went off and on briefly when moving the socket and bulb. This happened without taking the bulb out, and I could reproduce that symptom once or twice when tapping lightly on the right brake light bulb.
I also noticed that the right brake light bulb looked a little strange. There are two filaments and the lower/thicker filament was angled down in an odd way because one of the filament posts was a lot shorter than the other one. Just now, I looked online at Google Images of 1157 bulbs (my bulb) and none showed that.
Then, last night, I switched the bulbs, putting the weird (but working) right side brake light bulb on the left and the nonworking (normal looking) left side bulb on the right. After the switch, the right side brake light didn't work and the left side brake light did work. That, of course, would seem to indicate that the original normal-looking left side brake light bulb was probably bad since it didn't work when placed in the left side and also didn't work when placed in the right side.
But, I also thought that something may be weird with the odd-looking original right side bulb (including the possible loose connection and blinking off and on when tapped lightly). So, I went into Pep Boys and I bought two new bulbs and I put them both in -- one on each side.
Now, everything is working fine.
So, I don't really know what the problem was, but I wondered if it is possible that some type of defective bulb on the right side could cause any kind of short or something else when activated that would cause the opposite side brake light to not work. That seems unlikely to me, but who knows.
Also, I saved the two original bulbs, and today in the daylight I have been looking at them both very carefully with a magnifying glass to see if I could see a broken filament etc. Other than the odd-looking original right side bulb still looking weird, the filaments on both bulbs seem to be intact.
Hopefully, this fix from last night will last and I won't have to revisit this problem.
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TomR wrote:

Thank you for the update. Wish we still had free access to the mfg manuals.
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On Tue, 22 Dec 2015 17:32:49 -0600, Paul in Houston TX

Agree on the manuals, they helped me so much when I got my 03, 05, and 07. Not so much since.
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In typed:

UPDATE and a new question:
Well, it stopped working again after my fix. It is still the left brake light that does not work when stepping on the brake -- most of the time. A friend who followed me said that sometimes it would light up when I was stopping, and other times, it was not working.
I plan on taking it all apart again -- both sides -- and seeing if I can find a loose connection or a poor ground connection or whatever.
My question is, since when I had them apart before I could move the Right side bulb wires around and sometimes that bulb would go on and off. So, is it possible that a loose wire or connection on the RIGHT side could be causing the problem that I have on the LEFT side?
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TomR wrote:

If there is only one grounding wire for both lights then both would go off. Check the left socket wires, too.
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Every time I have chased problems like this it has turned out to be a grounding problem. I have had to take sandpaper to the inside of the socket and base. I've had to run an additional ground wire. Some don't even have a ground wire, just make contact with the metal frame.
"TomR" wrote in message
I have a 2004 Hyundai Santa Fe V-6 with a 3.5L engine.
People keep telling me that my left brake light does not light up when I step on the brake. The right brake light works as it should.
It seems to be an intermittent problem. Sometimes, when people say the left brake light is not working, I back up to a store front window and step on the brake and the brake light on both sides are working.
Another time, I found that the left brake light was not working so I changed the bulb. The old bulb didn't necessarily look like it was bad, but I changed it anyway, and both brake lights then worked.
Shortly after that, I got stopped by a cop for the same thing (no ticket, he just let me know it wasn't working) and I changed the bulb again and both brake lights worked. The old bulb looked fine, but I changed it anyway and the problem went away.
Then, soon thereafter, once again someone told me the left brake light wasn't working, and I checked and it was not working. This time, I looked at the bulb again and it looked fine like before. So, I just cleaned the terminals on the bulb and socket and put it back together. That didn't fix anything, so the left side brake light is still not working once again.
Tomorrow, I am going to take both sides apart, then switch bulbs between the right side and left side and test it again. My guess is that won't fix the problem since I assume both bulbs are good.
I assume that there must be a loose connection or wire someplace, but I don't know how to check for that. I was planning on buying a test light anyway since I am also having an electrical problem involving the rear lights on an old bomb 1989 GMC pickup truck that I own. I am wondering if I could use the test light to try to narrow down the source of the Hyundai left brake light problem, but I don't know what or where to test.
Can anyone suggest anything else that I could try?
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In

Thanks. I seem to have fixed the problem for now (see my other post), but if the problem returns I think the next step will be to try to see if there is a grounding problem somewhere.
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In typed:

FINAL UPDATE:
Thanks all. I finally fixed it.
I took both taillights off and unplugged all of the sockets from the taillights. Then, with the wires, sockets, and bulbs all hanging out loose, I was able move things around one bulb and set of wires at a time to see if I could find a loose connection and reproduce the problem. Since I was doing it myself, I cut a piece of wood to the right length and put it under the steering wheel and connected it to the brake pedal to keep the brake pedal depressed so the brake lights would be constantly on.
When moving the wires and sockets etc., I was able to narrow it down to a bad stop light socket on the left (driver) side. It wasn't a wire but instead was something in the socket itself which caused the brake light to go on and off when I moved the socket and bulb around. I tried cleaning and adjusting the bulb contacts etc and that didn't fix the problem. And, moving just the wires didn't reproduce the problem. So, it seemed like the problem was somewhere inside the brake light socket itself.
I went to a Hyundai dealer and they only sell the wiring harness itself for all 4 sockets, and do not sell just the one socket. So, I paid $33.50 and bought the new wiring harness. The one I bought looks like this: http://tinyurl.com/jxn2l8c
I had a problem figuring out how to access to the place where the wiring harness plugs in and then I found a YouTube video for installing a new trailer hitch wiring that showed me how to get to where the original taillight wiring harness plugs in. It involved removing part of the trim on the driver side inside the rear hatch area. Here is a YouTube video set to the part of the video that showed this. It shows the passenger side first and then the driver side. Here is the link:

http://www.youtube.com/watch?v=KLvK12BCORE&t=2m10s

I didn't do all of the removal of bottom floor parts of the trim etc that they showed beforehand and instead I just tried unclipping the driver side interior trim and tried just pulling the top of it back enough to try to reach in and disconnect the old harness and plug in the new one. In the process, by pulling back too far on the top of the trim, I managed to crack the trim in the lower left corner (oops). But, it is an old car and I don't really care that I botched that part up.
However, another choice that I had was that I could have just left the old harness in place and take just the new brake light socket off the new harness and use it to just replace the old brake light socket without having to open up the trim and replace the whole harness. But, I didn't do that even though it would have been a lot easier and quicker to do.
But, it is now fixed and I don't have to worry about being pulled over by the police for a non-working brake light (which had already happened a few times before and after my prior "fixes" where I had replaced the bulb etc).
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TomR wrote:

Excellent! Thanks for the update. I would have replaced the entire harness, too.
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