RTH for electrical novice - Headlight low beam

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Jul 26, 2020
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Juneau, Alaska
Non-specific to these trucks, but there is always someone knowledgeable online here. Good learner, understand the basics of grounding and shorted wires, but haven’t spent much time with electrical for this to be obvious to me. Was chipping ice off my driver-side headlight last week, and the little “shock” toggled the light off and then back on. A couple days ago it turned off while chipping ice, and haven’t been able to get it to come back on. Assumed weak connection somewhere at/near the connector/bulb. Given we are not far off from solstice, there is a lot of dark driving this time of year in AK, so lights are nice....

Bulb is good, fuse is good, high-beam and running lights both work. No issues with passenger headlight at all.

Wires going into each connector are different per side, but test light results are as follows

Good (passenger) headlight:

Grounded to body = terminal w/ thicker red/white wire lights up, but not thinner white/black wire

Grounded to either terminal in connector = other terminal lights up in both cases

Bad (driver) headlight:

Grounded to body = both terminals light up (both are red wires, one w/ yellow and other w/ blue tracer)

Grounded to either terminal in connector = no light on either terminal

So, what’s funky here? Grounded to body, getting power to both wires on the bad headlight, when it should just be the hot wire? Keep in mind the small shock of chipping ice off the lens is what affected it, so I can’t imagine it’s upstream from the connector, at least not far. Short? Ground?
 
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Joined
Jul 26, 2020
Messages
324
Location
Juneau, Alaska
Just found that the driver low-beam comes on when I activate high-beams, but now the driver highbeam itself doesn’t come on at all. When I tested a couple days ago, and also earlier today, highbeam had normal function, and the problem was isolated to the low beam. Passenger headlight function is still completely normal.

There is clearly some stream-crossing going on here on the driver side. WTF? Still looking for help, but for now I’m going to pull the highbeam bulbs and run the malfunctioning low beam by turning the high circuit on.

I hate electrical stuff.
 
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Comet

Knower of little, master of less.
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Subscribed. I do not have an answer. WTF is wrong with your rig? Blinker fluid or the the wires hanging off the battery? Something to do with a ground?

Obviously those smarter than me will chime in shortly.
 
Joined
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I have no idea. The one and only thing that occurred was the lowbeam turning off while chipping ice off the lens, which has to mean there is a bad/crossed connection right there that was affected by the small shock to the housing. But why now does the highbeam not work, and turning them on activates the low beam? Starting to feel like I’m on drugs

I’ve tested everything else and it all checks out. No other electrical gremlins with the truck whatsoever. Nothing else has happened other than chipping ice. I guess for now, at least I don’t have to worry about getting pulled over.
 

Comet

Knower of little, master of less.
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Toyota has a EDIT negative EDIT switch. Check grounds on each light. @jpoole obviously has schematics so I hope he helps.
 
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sacramento
I have no idea. The one and only thing that occurred was the lowbeam turning off while chipping ice off the lens, which has to mean there is a bad/crossed connection right there that was affected by the small shock to the housing. But why now does the highbeam not work, and turning them on activates the low beam? Starting to feel like I’m on drugs

I’ve tested everything else and it all checks out. No other electrical gremlins with the truck whatsoever. Nothing else has happened other than chipping ice. I guess for now, at least I don’t have to worry about getting pulled over.
Just a possibility...
Wire in the head light can break from the shock you gave it, then if power is on it can be shocked together (in effect re-welding). That's why you can sometimes get them to work by banging on the lights when they go out. Very temporary though. Obviously, only applicable to old school bulbs with filaments. Did this recently with a side lamp; lasted a whopping 5 minutes!
 
Joined
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Grounds seem to be fine.

The new development with highbeam switch at steering wheel turning on lowbeam, while highbeam itself no longer working at all, has thrown me for a loop. Before, it was isolated to lowbeam not working and kind of made sense, just had to figure it out. At least, I’m glad the passenger light still has normal function, isolating the issue to driver alone and not something bigger.

So there is the short length of 2 wires going to the low bulb, coming from headlight harness inside the corrugated tube that runs along top of grille. Wiring in the corrugated tube virtually never moves, but on occasion when changing bulbs or removing lights for other work, you do bend the two wires going into the housing. Understandably with age, that could get weak. Paired with the ice chipping/shock thing, I have a hard time believing the issue to be anywhere other than at the connector or that short length of wire. I’m going to let it go for tonight, but is my next move to slice open the sheath for those two wires and inspect them? Had a few beverages during my break, so starting to wander 😜

Brother is a skilled electrician with some auto knowledge, but has been MIA lately.
 
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I'm flattered to be looped in @Comet and do have schematics but no first hand experience with 80 series headlight electrical issues unfortunately.

Thanks to @BirfMark specifically, and everyone else who makes this forum possible generally, we all have access to the schematics. The following three manuals (downloadable from the urls/pages listed below) all include electrical information from troubleshooting guides to diagrams. They should all be keyword (like headlight) searchable though how you search will vary based on what software you open .pdf files with. The EWD is worth starting with in my opinion and among other things shows where possibly relevant grounds and splices are in the engine bay circuits.
To view all of the current 80 series related resources visit this page:
I recommend holding off on slicing into your harness until you are confident that it's necessary and in your ability to restore it correctly and avoid making things worse. My next step would be to focus on more testing until you get clear results or isolate the issue further. Since the issue has shown itself to be intermittent I'd likely include tests that coincide with gentle bumping and wiggling of involved circuits and components. I'd also try to rule out easy items including swapping the bulbs with spares or from the other side, checking/cleaning related grounds and connections, etc. though you may have already done this. Another idea is that if you can nail down which wire(s) are your grounds you can test them under load by creating a temporary circuit to a spare bulb with some loose wire from the battery/etc. If you run tests like this double and triple check before injecting power into your harness via any connectors as you could do serious damage (really). I'm far from an expert but I like to get repeatable and understandable results in my electrical tests and do that more often when I'm slow, methodical and double check my multi-meter, test circuits, etc. In any case you can likely isolate and understand the issue before you start any harness surgery.

Although I don't have the symptoms/diagnostics you described locked down mentally it does seem possible that you've got two wires/circuits that have shorted together or possibly a bad ground. I lean toward the bad ground mostly because in my experience they are more common and worth ruling out before going into other territory. If insufficient ground is present for bulbs they can sometimes seek out grounding in odd ways and display weird behaviors. Lights that work with odd switch combinations (like brake lights going out when running lights come on) can be the result of a bad ground at the bulb, oddly enough.

Ideally someone in the Mud mental repository has had your exact issue and will drop the two sentence quick fix soon, as so often happens here :)

Good luck!
 
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I figured it out and I don’t wanna talk about it. I’m confident in saying I’ve always been a pretty sharp person and a good learner, meticulous and often obsessive, but let’s just say I thoroughly won the idiot award today. Good lord, Spenser.

Regardless, thanks for those who chimed in, always appreciate this place and its members.
 

unclegit

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You should totally post the fix here. Mud sometimes builds a better idiot who could benefit from the obvious…..

Yes I’m talking about myself in the third person.
 
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I figured it out and I don’t wanna talk about it. I’m confident in saying I’ve always been a pretty sharp person and a good learner, meticulous and often obsessive, but let’s just say I thoroughly won the idiot award today. Good lord, Spenser.

Regardless, thanks for those who chimed in, always appreciate this place and its members.
Do please post the fix.


Many of us here have made stupid mistakes.



We promise that we won't make fun of you!



(much)
 
Joined
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Messages
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Juneau, Alaska
Haha I had meant to earlier. It started with a total brain fart, which should have immediately corrected itself and caused a chuckle, but instead I was fully locked in to this small (incorrect) detail.

Passenger low is easily accessible, while the high takes just a little fishing out. On the driver side, it’s the opposite - high is easily accessible, while low is kinda behind another connector. So what did I do? Well I was messing with the easy-access bulb on the driver side. The low, right? You know, because the low on the passenger side is the easier one, so this must be it. Yeah, nope, I fully committed to the brain fart and was messing with the driver highbeam the whole time. Derp, derp, friggin’ derp. How??? Why??? Pulled the correct bulb, and hey, look at that, the filament was jarred loose when I was chipping ice.

I clearly knew which was which, as the 9011 & 9012 bulbs were in their correct locations. So cheers to my dumb ass and another practice in humility. Couldn’t wait to tell the girlfriend and make fun of myself. But hey, no gremlins! Everything makes sense again 🤦‍♂️🤦‍♂️
 
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Messages
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Haha I had meant to earlier. It started with a total brain fart, which should have immediately corrected itself and caused a chuckle, but instead I was fully locked in to this small (incorrect) detail.

Passenger low is easily accessible, while the high takes just a little fishing out. On the driver side, it’s the opposite - high is easily accessible, while low is kinda behind another connector. So what did I do? Well I was messing with the easy-access bulb on the driver side. The low, right? You know, because the low on the passenger side is the easier one, so this must be it. Yeah, nope, I fully committed to the brain fart and was messing with the driver highbeam the whole time. Derp, derp, friggin’ derp. How??? Why??? Pulled the correct bulb, and hey, look at that, the filament was jarred loose when I was chipping ice.

I clearly knew which was which, as the 9011 & 9012 bulbs were in their correct locations. So cheers to my dumb ass and another practice in humility. Couldn’t wait to tell the girlfriend and make fun of myself. But hey, no gremlins! Everything makes sense again 🤦‍♂️🤦‍♂️
Sometimes you can't see the forest through the trees.
 

migz808

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Jan 24, 2017
Messages
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Non-specific to these trucks, but there is always someone knowledgeable online here. Good learner, understand the basics of grounding and shorted wires, but haven’t spent much time with electrical for this to be obvious to me. Was chipping ice off my driver-side headlight last week, and the little “shock” toggled the light off and then back on. A couple days ago it turned off while chipping ice, and haven’t been able to get it to come back on. Assumed weak connection somewhere at/near the connector/bulb. Given we are not far off from solstice, there is a lot of dark driving this time of year in AK, so lights are nice....

Bulb is good, fuse is good, high-beam and running lights both work. No issues with passenger headlight at all.

Wires going into each connector are different per side, but test light results are as follows

Good (passenger) headlight:

Grounded to body = terminal w/ thicker red/white wire lights up, but not thinner white/black wire

Grounded to either terminal in connector = other terminal lights up in both cases

Bad (driver) headlight:

Grounded to body = both terminals light up (both are red wires, one w/ yellow and other w/ blue tracer)

Grounded to either terminal in connector = no light on either terminal

So, what’s funky here? Grounded to body, getting power to both wires on the bad headlight, when it should just be the hot wire? Keep in mind the small shock of chipping ice off the lens is what affected it, so I can’t imagine it’s upstream from the connector, at least not far. Short? Ground?

I may have similar issue as yours on my 96 LX450. My left HL low beam does not work, high beam works. Light bulbs, HL relay and fuses are good. I am getting power on both pins while on low beam on the left HL. I don't think think that should be the case. On the right HL only one of the pins has power, that I believe is normal. Now the weird thing is if I take out the fuse for the right HL and keep the left HL fuse, my left HL low beam will work. Hoping my situation as well as yours is just a simple ground issue.
 
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I may have similar issue as yours on my 96 LX450. My left HL low beam does not work, high beam works. Light bulbs, HL relay and fuses are good. I am getting power on both pins while on low beam on the left HL. I don't think think that should be the case. On the right HL only one of the pins has power, that I believe is normal. Now the weird thing is if I take out the fuse for the right HL and keep the left HL fuse, my left HL low beam will work. Hoping my situation as well as yours is just a simple ground issue.
You're missing a ground connection on the left low beam. When you remove the fuse for the right side, the left is grounding through the filament of the right bulb. Remember, a bulb filament is nothing more than a piece of wire. While the left and right have separate ground points to the respective inner fenders, there is a common point further upstream.
If you download the LX450 EWD in the resources section, it will become clear.
 
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migz808

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Messages
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You're missing a ground connection on the left low beam. When you remove the fuse for the right side, the left is grounding through the filament of the right bulb. Remember, a bulb filament is nothing more than a piece of wire. While the left and right have separate ground points to the respective inner fenders, there is a common point further upstream.
If you download the LX450 EWD in the resources section, it will become clear.

@jonheld Thanks for the input. Would that also be causing both pins to have power on the left HL connector with low beam on?
 

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