Headlight puzzle


I’ve got a headlight issue that I’m having a hard time troubleshooting. I’d be grateful for any suggestions.

Last weekend I noticed the headlights in my 2005 Toyota Corolla were out. The high beams and the fog lights are fine. Also, it might be useful to know that this model Corolla has daytime running lights meaning that the headlights are usually on no matter what. I believe they get brighter when the car senses that it is dark outside.

So, I figured it was a fuse. It turns out this car has a fuse for each low beam headlight and they both look fine. Then I checked the bulbs and they look fine too. I’m ruling both these out because they look fine and I just don’t see both left and right going out at the same time for either of these.

I don’t think it’s the switch because the daytime running lights aren’t working either.

I guess it could be a relay. I looked up an electrical diagram of these headlights and promptly learned that I don’t know how to read one of these. I wanted to learn if there is a relay that just the low beams run through and not the fog lights and high beams.

Someone suggested that it could be the daytime running light relay and that all the lights run through that before they get to the switch. I’m not sure about that.

Any thoughts would be greatly appreciated.


P.S. I’m attaching the electrical diagram in case that is useful

I can’t open the wiring diagram you show. So I went to my online auto repair service. And the wiring diagram there shows that the Daytime Running Light relay also controls the Low Beam relay. So if the DRL’s and the low beams aren’t working I’d say the problem is with the DRL relay.


According To The Diagram (Click On It To Enlarge), The DRL Relay Runs To The Right & Left Headlights.

I’d find a relay in the car’s fuse/relay panels with an identical part number to the DRL relay and unplug them and swap them temporarily to see if the headlights light up.

If a different identical relay makes it work, I’d swap them back where they were and then go buy/order a new relay for the defective unit.


The diagram opened for me but it’s so fuzzy that all letters and numbers are incomprehensible and I can’t read them even with a magnifying glass. A few wire leads seem to run off into other pages which are not shown.

There does seem to be a large number of fuses involved in the lighting circuit and I would suggest checking every fuse you can find with a test light or VOM,
Will dig around a bit and see if I can find a clearer schematic.

I’m going to suggest that, yes indeed, headlights can go out together. It is not common, but I have seen it happen a few times. Just as it is common for bulbs to go out within days of each other.

Ok thanks everyone. I’ll get a test light and check the fuses in more depth.

The schematic was kind of illegible to me but I wasn’t sure if that was just because I don’t know anything about these schematics.

In the event that it is a DLR relay, I’ve been googling and looking for a “2005 Corolla Daytime Running Light Relay” and I’m actually not really finding a part by this name. I’ve found like one thing on ebay but nothing on what I consider to be legit sites light Autozone. Does this also go by a different name?

Just to follow up. Looks like these do exist but they are around $160. Is it possible to just bypass this relay altogether and just operate the headlights via the headlight switch?

They call this a relay but looking at the wiring diagram it’s more like a contol module which explains why it costs so much. http://www.rockauto.com/catalog/moreinfo.php?pk=3782376&cc=1433059

I don’t see how you can easily take this relay out of circuit as it not only controls the low beam relay, but also supplies power to all the other exterior light relays on the vehicle. If it were me, I’d bite the bullet and replace the relay.


Ok thanks. It probably pretty clear at this point that I don’t do a ton of work on cars. Can I do this myself?

Also, does this part look like it would work? It looks the same and says “relay running light module.” There are no other running lights aside from daytime running lights correct?

Edit: This post was missing the link http://www.ebay.com/itm/310684465002?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649

Oh and thanks to everyone that has answered. I appreciate it.

Plus, one more double check.
You can bench test ( not just look at ) the headlight bulbs on any 12v power source with jumper leads .
Looking into the bulb locate the one terminal that contacts both filiments, that’ll be your ground or ( - ).
The other two will each be ( + ) dim or bright.
Wait, now I see it’s a 9006 single filliment bulb…only two terminals. EITHER can be negative or positive and pass a bench test.

Don’t rule out the bulbs because they look fine. Buy a new pair and try them. You will need a new pair someday anyway. Read bulb handling precautions before installation.

I just took a light tester to all of the fuses and everyone works but the low beam fuses. I’m getting no response from either terminal on those. Stop me if I’m wrong but that suggests that it is the DRL relay and definitely not bulbs or fuses.

The DRL relay sends voltage to the primary side of the dimmer relay which closes the contacts in the dimmer relay. When the contacts in the dimmer relay closes it then sends voltage to the two fuses for the low beam headlights.


After checking your helpful wiring diagram it looks to me that the low beams are controlled through the relay marked HEAD RELAY. There is a 40 amp fuse that supplies power to the relay and it is most likely located in the panel under the hood. Check that fuse and make sure power is getting through it. If that is ok then you could try bypassing the relay contacts to see if that will get the lights to work and will verify that part of the wiring is ok. The relay contacts may be at fault. I assume the relay is getting turned on when it should be. The relay control lead ties to the lead marked H on the right side of the drawing and doesn’t show how the connection to ground is made to turn on the relay. Grounding that lead manually will activate the relay if that is required. If the relay seems to be the problem try to swap it with another one of the same style.

Tester you are a little over my head there.

Cougar, thanks for the ideas. It turns out that the Head relay is the same part as the Dimmer Relay. I tried swapping them and got no result. You are right, there is a 40 amp fuse labeled Head Main. I’m not sure how to test it as it has no terminals but it appears to be intact.

Just to be more thorough about my fuse testing. There are four fuses in total that aren’t reading at all with the light tester. Head LH UPR, Head RH UPR, Head LH LWR, and Head RH LWR. I figure LWR is for daytime lights and UPR is for headlights.

So… I still believe Tester, and others, saying that it is the DLR Relay. I located it under the steering wheel and believe I can swap in a new one pretty easy.

Another question is what are peoples’ thoughts on buying a used one of these off of ebay to save a hundred bucks.

I’d be careful buying vehicle electronic components off EBAY.

I knew a guy who would pull parts off cars at a U-PULL-R-PARTS yard and then sell them on EBAY. Never tested the parts before they were sold. So who knows how many people got screwed from defective parts?

But that looks like the module.


I cannot tell you how many people throw hundreds of dollars at what if’s and will not even try a simple light bulb swap. Looks like we have another. Did you take the bulb out and look at it? some times the filiment breaks, tapping on it you will see one side or the other move not both, my philosophy is to start simple, and probable, throw your money at whatever but if at the end of the day it is bad bulbs do not blame car talk.

I have a 40 year old gas stove with double ovens.
One day I turned on the oven lights (one switch for both ovens) and neither light came on.
I mindlessly removed the knobs and front panel. A messy job with decades of grease inside.
I checked for power: good, I tested the switch: OK.
THEN I took out a light bulb and tested with an ohmmeter: open!
I checked the other bulb" open!