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High Mounted Stoplight


jmwgomz
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I can't seem to figure outh why there is no electricity going to the high mounted stoplight on my 1991 LS400. I recently noticed that a bulb was out. I went to the dealer and bought two new bulbs for it and they do not work. I put in the old bulb which "WAS" working and it didn't light either. I then checked if there was any electricity going to the wires when I pressed the brake pedal and there wasn't. I checked the brake fuse and it seems to be fine. All of the other lights work fine. Does anyone have any ideas?:wacko:

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Wow - that is wierd. How did you test the voltage going to the brake-light?

All I can think of is a shorted wire somewhere. I would start by testing the other lights and independently testing the lightbulbs with batteries. Other than that, I'm at a complete loss.

A wiring schematic for the brake light is attached if you need it.

post-15234-1109619479_thumb.jpg

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I asked the identical question about 6 months ago on the forum, and never got an answer that helped. I guess the problem is in the wiring. I know the wiring from the light goes to some sort of electrical distribution box that I can see behind the trunk interior wall on the passenger side. I would guess that this might be where the problem lies, but I'm not technical enough to mess with it.

So I drive w/o the highmount. No problems to date. Best of luck.

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WOW! Thanks for the schematic Econ. I'm having trouble figuring this one out. I don't want to tear the car appart so I am sticking to the simplest solution (which most of the time resolves the issue). Someone must have some idea of what may be happening here. Please let me know! :wacko: :(

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So I took the back seat apart ( :censored: ). I now "KNOW" that the stoplight wiring does not go to that box in the trunk. I still can't figure out why there is no electricity to the bulbs. I'm hoping that someone can look at the schematic that Econ posted and tell me where the fault would have to be in order to cut off only the high mounted stoplight bulbs. Like I said earlier, only the high mounted lights don't work, all the others work perfectly. Thanks again guys!

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Well, a quick browse at the schematic makes me think that there are 2 places you could have a problem. The light failure sensor could be having a problem and the current to the light could be interrupted. Or there's a wiring issue in the high mount circuit after the light failure sensor.

According to the schematic, there's a green wire with a yellow stripe coming from the light failure sensor and leading to the brake light. You'll want to test those wires to ensure that there's any current coming from the light failure sensor.

If there isn't, then the sensor is probably your issue. If there is, then you'll want to try the white wire with a black stripe coming from the switch. That's the ground wire. Follow it until you make sure it's spliced into another ground wire (also white with a black stripe). It might or might not be close to a harness that is also spliced into this ground.

The light failure sensor is mounted on the body (I think) behind the left-hand quarter trim panel in the rear. It's smallish and has 2 green wires with white stripes, one red wire with a blue stripe and one violet wire with a green stripe leading to (or from) it. They might be wrapped in electrical tape, and the red/blue and violet/green wires are probably connected to a harness that is close to the sensor (though it might not).

I assume you're using a multimeter to check the circuit for power? Let me know if this isn't helping you.

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:D SUCCESS! :D I tested the sensor with a multi-tester. Found that only the G-Y wire that leads to the high mount stop light was not working. Opened up the sensor. Found where it had been blown out. I don't have soldering tools or experience so I took it to a local T.V. repair shop. An older gentleman (really nice guy) did it for free! I insisted on paying something but he would not allow it (I think I am going to buy him lunch later today). Got back, put the sensor back in and everything works perfectly.

Econ, thanks a million. I'm going to have to buy you a beer next time you are in

San diego! :cheers: Thanks again!

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Man, I am glad you nailed that one! Kudos to you - you're the one that took it all apart, twice!

Thanks for posting up the source of the problem here, I'm going to make a mental note myself as this could have been quite the gremlin. And if I'm ever in San Diego, I'll be sure to let you know. It'd be great to have a beer and just stare at the beautiful (and working) high mount stop light. :cheers:

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Sure Tex,

I found my sensor in the trunk of the car. Direcly behind the diver's side post which holds the trunk lid on the car. The sensor is held on to the back of the tunk by a frame. The sensor will come right off if you push in the plastic clip which holds it in position. (If you position yourself standing behind your car, looking into the trunk with the trunk lid open, you can find the sensor on the left side of the back wall directly behind where the trunk lid connects to the car. You have to remove the (in my car, gray) lining in the back of the trunk in order to reach the sensor).

I took off the sensor and followed the schematic to test it and make sure that it was in fact only this wire that was malfunctioning (which I already knew because these were the only lights not working). Once my suspect was confirmed, I opened the sensor and followed the path that the current leading to this wire took. I was quickly able to identify where the problem was with just a visual inspection. If you have a similar problem you should be able to see some type of interruption in the path of the current within the sensor.

Remember that my car is a 1991; there may be some differences with your car. I suspect that if your re-feuling door is on the driver's side of the car, then the sensor will (probably) be in the same place but on the passenger's side of the car. The sensor is almost a cube (probably about 2"x2"x2") and mine had "TOYOTA LIGHT SENSOR" written on it.

Let me know how it goes and if you need more information. Good luck with the repair.

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Thanks, jmwgomz. I think the box is the same one I referenced in my first response here-but I didn't have a clue what it was. I called it an "electrical distribution" box. Now I can check it out. Was it hard to remove the crap in the way of the box?-ie the trunk liner, etc.

Thanks. I'll be busy tomorrow.

Tex

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