Tail light trouble... Please Help!!

[teedoff00]

Ok, I have already posted some info about this ongoing problem of mine. For more info on what the history is here's the original post http://www.supramania.com/forums/showthread.php?t=68682
So to summarize, my tail lights/park lights/interior lights haven't been working, due to the fact when the light control switch is engaged the fuse immediately blows. So today I went through my tail light panels to check for corrosion I found a little but I cleaned all the sockets and bulbs etc. I then went ahead and put a new fuse (15 amp) and turned the running lights on. To my surprise everything turned on and was functioning properly. However, this had happened before so I wanted to make sure it was fixed, (because once before I placed a 20amp fuse and it lasted for about 10 mins.) so I tested the connections with my voltmeter. I wasn't getting a very good reading so I stupidly switched the ground with the B+ on the voltmeter to see if the reading changed. My tail lights then went out. Now for the part I am having problems with... I checked the fuse and it hadn't blown like I expected when the tail lights went out. The interior and park lights are still working. The brake lights work, along with every other bulb/filament in the two rear panels except for the tail light filaments.

So here's what I have tried:
1. Checked the fuse, replaced with new, no difference. (no tail lights everything else fine.)
2. Checked the common ground near the hatch release and cleaned, and sanded off the paint under the bolt to insure a good ground. No change.
3. Swapped bulbs to see if maybe (appears I still have my original tail/brake bulbs!!) they were having issues. No change.
4. Got a reading of around 12 Volts from the brake side of the bulb sockets when the brakes were depressed, but no voltage at all when connected to the electrode that services the tail light filament.
5. All bulbs have good filaments including the turn and rear back-up lights.

Here's what I figure it could possibly be and where I most need your guy's input:
1. I know the tsrm says there is a tail light relay in the kick panel. Could this go bad? Did my switching of the voltmeter leads cause it to blow even though the fuse didn't? Does it only control the tail lights only, or the filaments in the bulbs that are set for tail lights?
2. Is my wire (b+), although what was possible to check I did with out ripping off all the side panels, seats and carpet, is it somehow frayed, or exposed? I don't know how this would be the cause since my tail lights did come on, however briefly.

So what do you guys think? What could I try? Am I missing anything?
All suggestions and comments are welcome! Thanks a lot, sorry this is long and I hope it is a post worth your time.

 

[Supraboy89]

Ok, I have already posted some info about this ongoing problem of mine. For more info on what the history is here's the original post http://www.supramania.com/forums/showthread.php?t=68682
So to summarize, my tail lights/park lights/interior lights haven't been working, due to the fact when the light control switch is engaged the fuse immediately blows. So today I went through my tail light panels to check for corrosion I found a little but I cleaned all the sockets and bulbs etc. I then went ahead and put a new fuse (15 amp) and turned the running lights on. To my surprise everything turned on and was functioning properly. However, this had happened before so I wanted to make sure it was fixed, (because once before I placed a 20amp fuse and it lasted for about 10 mins.) so I tested the connections with my voltmeter. I wasn't getting a very good reading so I stupidly switched the ground with the B+ on the voltmeter to see if the reading changed. My tail lights then went out. Now for the part I am having problems with... I checked the fuse and it hadn't blown like I expected when the tail lights went out. The interior and park lights are still working. The brake lights work, along with every other bulb/filament in the two rear panels except for the tail light filaments.

So here's what I have tried:
1. Checked the fuse, replaced with new, no difference. (no tail lights everything else fine.)
2. Checked the common ground near the hatch release and cleaned, and sanded off the paint under the bolt to insure a good ground. No change.
3. Swapped bulbs to see if maybe (appears I still have my original tail/brake bulbs!!) they were having issues. No change.
4. Got a reading of around 12 Volts from the brake side of the bulb sockets when the brakes were depressed, but no voltage at all when connected to the electrode that services the tail light filament.
5. All bulbs have good filaments including the turn and rear back-up lights.

Here's what I figure it could possibly be and where I most need your guy's input:
1. I know the tsrm says there is a tail light relay in the kick panel. Could this go bad? Did my switching of the voltmeter leads cause it to blow even though the fuse didn't? Does it only control the tail lights only, or the filaments in the bulbs that are set for tail lights?
2. Is my wire (b+), although what was possible to check I did with out ripping off all the side panels, seats and carpet, is it somehow frayed, or exposed? I don't know how this would be the cause since my tail lights did come on, however briefly.

So what do you guys think? What could I try? Am I missing anything?
All suggestions and comments are welcome! Thanks a lot, sorry this is long and I hope it is a post worth your time.

sounds like to me you have a short thats grounding out at times causing the fuse to blow. maybe a open wire or a pinched wire

 

[teedoff00]

sounds like to me you have a short thats grounding out at times causing the fuse to blow. maybe a open wire or a pinched wire

Yeah I thought of that, but like I said, the fuse hasn't blown since I cleaned the small corrosion deposits I found. The problem is the tail lights don't light. All the other park/gauge lights that run off the same fuse work. (ran for about 30-40 mins.) Thanks for your input!

Does anyone know if the tail light relay controls more than just the tail lights themselves or if it is also linked, like the fuse, to the park lights, etc.???
Thanks again!

 

[Frank Rizzo]

The light failure sensor controls the rear side marker lights, the tail lights, the brake lights and the license plate lights.

It does not control the rear turn signal lights or reverse lights.

This sensor is in the rear of the car, below the driver's side rear tail light harness, it has a dark blue connector on it. Take it apart and check for corrosion.

 

[jetjock]

Don't go postal on me Frank but in the interest of accuracy the box monitors (not controls) only the tail and brake lights. The rear markers and license plate lamps aren't involved.

 

[teedoff00]

Don't go postal on me Frank but in the interest of accuracy the box monitors (not controls) only the tail and brake lights. The rear markers and license plate lamps aren't involved.

Ok so I had a little time to look at the wiring diagrams in the TSRM and from what I could tell the only thing that has a direct path to the tail lights only is the light failure sensor. So the Tail light relay along with the tail light fuse supply power to all the park/interior/license plate illumination, etc. So as far as I could tell either the light failure sensor (just the put for the tail lights because brake lights still work) must be malfunctioning or there is something missing. What should I try? Thanks jetjock and frank for your input.
What do you guys think?

 

[jetjock]

I didn't read the entire thread but if the markers and brakes work but the tails don't either the LFM is bad, the wiring after it is open, or you're missing a ground. That's assuming the bulbs are OK. That said I'm puzzled about something: since you appear able to interpret the schematic why aren't you troubleshooting this simple problem by doing circuit analysis with a meter or test light?

 

[teedoff00]

I am sorry if I see ignorant, I just have been working on this for quite some time and can't get it to fully work. So if the Light Failure Sensor is bad then this would cause the filaments in my tail lights to not light, correct? (since it monitors and not controls, but from what I can tell is the only thing in the direct path of the tail light filaments). I have used my voltameter to confirm there is no voltage going into the electrode for tail lights in the socket. I have also confermed that there IS voltage to the brake light electrodes. So like JJ said it lies between the LFS and the bulb itself (which is good, because I replaced all of them!!), the ground as stated before was refinished and is good, and the wire from the LFS to the bulb is in good shape (no cracks, no exposed wire.) So by process of elimination it has to be the Light Failure Sensor, right? (dont have another one to swap in at the moment to test and the TSRM doesn't metion how to test it...) This is assuming it disrupts the B+ from the tail light filaments if it is bad...
Thanks for your help JJ!!

 

[teedoff00]

Ok sorry JJ...
I was able to find the testing instructions for the Lamp Failure Sensor and I turned on the running lights and got voltage from the harness side of the tail light lead. So since I got no voltage at the electrode in the socket, I guess that means I need a new sensor. So hopefully that will work. Thanks for all your help guys!

 

[jetjock]

Well, why don't you just jumper it and see if the tails come on? Pins 10 (green wire) and 4 (green with red stripe). The box can be left connected or not.

 

[teedoff00]

Yeah I thought of that since I don't know how hard it is going to be to get a replacement for the car so. That will also definitely tell me if it is the box. Thanks a lot JetJock, I appreciate your help!

 

[jetjock]

Good luck. If they come on plug the connector back into the box (so your brakes lights will work) and put the jumper in the back side of the connector until you get a new box. They come up on ebay from time to time for very cheap. There's different types so make sure you get the right one. I'd bet a member has one they'll part with. Course, you could also jumper pins 7 and 1 (brake lights) and toss the box in the trash.

Or open it up and have a look. There's a spot where they typically fail that can be easily repaired. CRE has a long thread about it. Search.

 

[teedoff00]

Good luck. If they come on plug the connector back into the box (so your brakes lights will work) and put the jumper in the back side of the connector until you get a new box. They come up on ebay from time to time for very cheap. There's different types so make sure you get the right one. I'd bet a member has one they'll part with. Course, you could also jumper pins 7 and 1 (brake lights) and toss the box in the trash.

Or open it up and have a look. There's a spot where they typically fail that can be easily repaired. CRE has a long thread about it. Search.

Yeah I opened it up to clean it and inspect, but from what I could tell the resistors looked good, so I will have to see what I find. I will search for CRE... I found one on ebay from an 88 supra and will probably get it after I make sure it is in fact the box tomorrow.
Thanks again for your help Jetjock.

 

[3p141592654]

Typical LFM failures can be repaired. Find out more here.

http://www.supramania.com/forums/showthread.php?t=46770

 

[teedoff00]

Yeah I bought a box off of Ebay for 25 bucks shipped. Then after I already purchased it I thought to myself, why do you need that stupid sensor anyway, I am constantly looking things over, the sensor is usless... But yeah, it jumpered till it gets here, and everything is working great! I am having a little bit of buyers remorse, but...
on a more serious note, thanks to everyone who responded to this pretty simple (at least now!!:3d_frown issue especially JetJock who coached me though it.
Big thanks!

 

[Dr Chill]

I had to Jump mine .
You do have to have it plugged in
Also your light on the dash will show that you have a blown bulb somewhere .(tail Light Out)
but all of mine work fine .