Why would wires in Lamp Failure Sensor Overload?

[oxymoron]

It looks like I'm going to have to take my 1993 Camry to a mechanic to find out what's wrong, but before that I wanted to see if anyone has any other ideas about why this is happening so that I can at least give them idea.

As I said before, the tail lights stopped working. The brake lights do work. I looked inside the Lamp Failure Sensor and one of the connections in the tail light relay was blown and the board was burned. It looks like this:




Resoldering the connection fixed the tail lights, but the wires overloaded and burned again. I got a working replacement sensor and it overloaded exactly the same way, so the problem must be somewhere else in the system.

Can anyone give me any ideas about why these two specific wires inside the box would be overloading, and why it's happening specifically at the point where they connect? None of the wires in the trunk show any signs of burning or breakage and no other parts of the circuit board appear to overheat (including the other parts that carry the tail light current). (EDIT: This isn't true. The other parts of the board that carry the current have also singed a bit, it's just not as noticeable.) If there's too much current passing through the tail light wires, why isn't the tail lamp fuse breaking? Is there any obvious reason why there would be too much current going through the wires if that's what's happening?

[Stillrunning]

Didn't Mike Gerber already suggest inspecting the wire loom where it flexes at the trunk to see if there are some frayed wires. Did you do that?

[Eye8Pussies]

I would say that it was a separate wire being grounded on the chassis....

but as you said though....doesn't answer why the fuse isn't blowing.


the only time that I know of things grounding and melting circuits instead of blowing a fuse is when there is a capacitor involved- then the current moves so fast that it doesn't blow the fuse. I had this happen several times with my amps (my mistake for not discharging my caps first), but that was with a 1 Farad capacitor

[oxymoron]

Originally Posted by Stillrunning

Didn't Mike Gerber already suggest inspecting the wire loom where it flexes at the trunk to see if there are some frayed wires. Did you do that?

Like I said in my post, I checked all of the wires in the trunk (including the ones on the hinge) as much as I was able to and couldn't find anything wrong with any of them.

Originally Posted by Eye8Pussies

I would say that it was a separate wire being grounded on the chassis.... but as you said though....doesn't answer why the fuse isn't blowing.

the only time that I know of things grounding and melting circuits instead of blowing a fuse is when there is a capacitor involved- then the current moves so fast that it doesn't blow the fuse. I had this happen several times with my amps (my mistake for not discharging my caps first), but that was with a 1 Farad capacitor

That make sense, but even if it was something to do with the capacitors, it still doesn't explain why the second Lamp Failure Sensor also overloads and burns. Unless both of them are faulty in exactly the same way?

The only other thing I can think of is there being something wrong with the plug that attaches to the sensor. Is that possible? If the plug was somehow causing too much electricity to enter those pins on the sensor (which I don't even know if that's possible, I'm not an electronics person ), and all of the extra electricity was being released inside the sensor as heat (so it was being built up and released all inside the sensor), would that cause the fuse to not to blow?

[dc_98_cam]

There could be an internal short within the external connector socket.

If you can get a volt-ohmeter, test the continuity between the white with black stripe wire, and each other individual wire on the plug. You should see no indication of continuity, that is open circuit ... just testing the socket disconnected from the lamp failure sensor, no power applied, lights turned off. .... The VOM negative or black lead is touched or clipped to the W-B wire contact ... and then test each of the other wires with the positive VOM lead, one at a time, with the VOM set to measure resistance, .... say on the highest scale. ... VOM meters can usually be found at economical prices ..... a few dollars. ...

If your meter is analog...with a needle, it should swing full scale, all the way over. If the VOM is digital, it should read a high number when you test each wire.

If you do find continuity between the white with black stripe wire, and any of the other wires going into the plug socket, then you know something is wrong.... internally within the socket.

Also use the VOM in continuity mode to check that the white with black stripe wire is in fact making contact with the chassis ground. Do this first. maybe. If this wire were not properly connected to chassis ground, it might contribute to the basic problem. ... One test lead is placed on a clean, bare metal chassis ground ... maybe a screw or bolt, and the other lead on the white with black stripe metal socket contact.

The circuit diagram shows 5 wires going into the sensor: green, light green, yellow, yellow with green stripe, and the chassis ground wire, which is white with black stripe. ... The green and light green are the main current carrying wires. The others are part of the lamp signal activation circuit. ... The larger band looking metal piece on one end of the board is a current shunt .... which just passes the main tail light current load, and also produces a measurable voltage that is used to signal the status of the tail light current. .... and in effect, is used to control the on/off condition of the lamp warning light.

The circuit diagram is shown here. See p. 145.
It is not a complete diagram, but gives some idea as to the layout and function of the lamp failure sensor.:
http://www.camrymanuals.com/index.ph...=106&topicid=0
... see gen 3 section .... wiring schematic pdf.

[oxymoron]

Thank you so much dc_98_cam! I was trying to find diagrams like those. Unfortunately I wasn't able to get a voltohmeter in time and we had to take the car to the mechanic because we couldn't wait any longer to have it fixed. I wasn't able to go when the car was dropped off so I sent a list of the things that I had tried and that I had found out so they would have an idea where to start. I made it pretty clear that the replacement sensor would make the tail lights work but would overheat and burn. I guess they didn't read the list though because when I called after the car had been there all day the person I spoke to told me that not only had they put our replacement lamp failure sensor in the car to test it, but they had actually taken the sensor out of another Camry they were working on and put it into our car and tested it. And he informed me that the tail lights worked with both of those boxes so the original box must be "faulty". This is a bad sign, right? I hope they didn't ruin somone else's lamp failure sensor. He also said someone had put "incorrect bulbs" into the tail light fixtures - he said there were "double filament bulbs" in the tail lamp/brake light sockets and that they were supposed to be "single filament bulbs". I explained that it says in the car's manual that the tail/brake lights are supposed to use 1157 bulbs so there was no problem. He also said the "technician" he was working with had opened the original sensor (the one that's burned up) when I asked if they had looked inside and he said he didn't seen anything wrong with it.

[dc_98_cam]

.... interesting. Not sure if I understand the situation completely.

If you find out anything else ....

[Stillrunning]

Originally Posted by oxymoron

He also said someone had put "incorrect bulbs" into the tail light fixtures - he said there were "double filament bulbs" in the tail lamp/brake light sockets and that they were supposed to be "single filament bulbs". I explained that it says in the car's manual that the tail/brake lights are supposed to use 1157 bulbs so there was no problem.

This makes no sense, double filament bulbs will not plug into single filament sockets. I did however look up 1157 and 1034 bulbs on the Sylvania web site. Both are double filament and for brake/signal. The 1157's draw 2.1 amps while the 1034's draw 1.8 amps. I'm not sure if this is enough to blow your light sensor or not, but incorrect amp bulbs could explain the problem. My Camry uses 1034's as replacements. Are you sure the manual says 1157?

[oxymoron]

I didn't realize I never came back and explained what happened (better late than never I hope, in case someone else has this problem in the future, although there's not much chance of that ).

You guys will never believe what the problem was. The connection end of one of the 1157 bulbs I put in somehow "mushroomed" out (I have no clue how, neither did the mechanic) and expanded to it was touching both sides and caused a short circuit. It had absolutely nothing to do with the reason the original Lamp Failure Sensor burned up, it just coincidentally caused exactly the same thing to happen. Also I'm convinced the mechanic was wrong, there was nothing wrong with the type of bulbs I put in, one of them was just faulty. He never admitted it, but they did put in exactly the same kind of bulb.