[WUTANGSUUU]

Fix one thing, and the next thing breaks. As I stated, my tail lights do not work anymore, but pressing the brake will illuminate those very same bulbs.

I've checked the bulbs, all of my fuses checked out, and my wiring SEEMS fine. The low filament on the bulbs are just not illuminating. I do not know what else to check.

Every single other light on my car works, all the way down to my license plate lights.

I can't find any wiring diagrams online for my car. Where should I take this thing to get it fixed? A normal shop?

I really need to get this fixed because when I commute home on the highway everyday, it's dark out and I can't afford to get tagged by state troopers.

 

[93celicaconv]

Do your front side marker lights (running lights) come on when you turn your light switch on?

If they do, and only your rear tail lights don't come on, I would look where your ground wire is on that wiring harness for your rear tail lights. It seems to me your ground wire for the rear running lights in your tail lights is open circuited.

I have manuals for the 5th Gen Celicas (1990-1993), but not for your specific 4th Gen vehicle, otherwise I would tell you were that ground wire connection to the body is located.

Actually, I found a wiring diagram for an ST165 (an All-Trac version of yours). I believe the rear tail light wiring on the All-Trac is the same as you have - I don't know if you have a lamp failure sensor on yours though. What I would do is, I would check the W-B (white wire with black stripe) wire coming from one of the rear tail light wiring harnesses (not the same color wire coming from the brake light wiring) and see if the W-B wire has continuity to ground. If it does not, splice in a new wire and find a good ground in the trunk area to attach the other end of that new wire to, then see if that solves your problem (as you state, just the rear tail lights don't work - everything else does).

 

[WUTANGSUUU]

Do your front side marker lights (running lights) come on when you turn your light switch on?

If they do, and only your rear tail lights don't come on, I would look where your ground wire is on that wiring harness for your rear tail lights. It seems to me your ground wire for the rear running lights in your tail lights is open circuited.

I have manuals for the 5th Gen Celicas (1990-1993), but not for your specific 4th Gen vehicle, otherwise I would tell you were that ground wire connection to the body is located.

Actually, I found a wiring diagram for an ST165 (an All-Trac version of yours). I believe the rear tail light wiring on the All-Trac is the same as you have - I don't know if you have a lamp failure sensor on yours though. What I would do is, I would check the W-B (white wire with black stripe) wire coming from one of the rear tail light wiring harnesses (not the same color wire coming from the brake light wiring) and see if the W-B wire has continuity to ground. If it does not, splice in a new wire and find a good ground in the trunk area to attach the other end of that new wire to, then see if that solves your problem (as you state, just the rear tail lights don't work - everything else does).

I see. Though, do I read this wiring diagram left to right? I see where each component is, but how I locate these on the orientation of the wire harness on the car?

My front side markers are actually not illuminated, I noticed this morning. So thats two sets of lights that are not functioning.

I drove it to work this morning and found that the “tail light failure” light is now illuminating on the dash. It wasn’t before when I investigated the issue a couple days ago. This light came on months ago when my taillights DID work, and I simply replaced a blown bulb.

I don’t believe there is a lamp failure sensor in this car, but I'm not entirely sure either since I'm seeing conflicting information online.

 

[93celicaconv]

OK, so you have more lights not working beyond the running lights in your tail lights. Your front side markers also don't work. Do your rear side marker lights work? Can you verify again that your two license plate illumination lamps work? Do all the illumination lamps inside the car work (radio illumination, cigarette lighter illumination, defogger switch illumination, cruise control on light in your instrument cluster, shifter illumination (if you have an automatic transmission with a console shifter), hazard switch illumination, heater controls illumination, glove box illumination lamp, instrument cluster back lighting)?

If none of these work, you will want to check your 15A tail fuse to see if it is working properly (don't just look to see if the fuse is blown - it may look intact but be open circuited - check if the fuse has continuity or not).

Your instrument cluster, having a lamp on as you show in your picture, is an indication that you do indeed have a light failure sensor (that is what turns the instrument cluster lamp you show on if it senses a problem).

 

[WUTANGSUUU]

OK, so you have more lights not working beyond the running lights in your tail lights. Your front side markers also don't work. Do your rear side marker lights work? Can you verify again that your two license plate illumination lamps work? Do all the illumination lamps inside the car work (radio illumination, cigarette lighter illumination, defogger switch illumination, cruise control on light in your instrument cluster, shifter illumination (if you have an automatic transmission with a console shifter), hazard switch illumination, heater controls illumination, glove box illumination lamp, instrument cluster back lighting)?

If none of these work, you will want to check your 15A tail fuse to see if it is working properly (don't just look to see if the fuse is blown - it may look intact but be open circuited - check if the fuse has continuity or not).

Your instrument cluster, having a lamp on as you show in your picture, is an indication that you do indeed have a light failure sensor (that is what turns the instrument cluster lamp you show on if it senses a problem).

Rear side markers are still functional. My plate lights illuminate as well.

All of my illumination inside the vehicle functions as it should, cigarette lighter etc, the instrument cluster lights up.

 

[93celicaconv]

You may want to get a replacement lamp for your front parking/running lights and see if a new lamp fixes the problem up front. Perhaps do the same for the rear tail lights (your brake light filament in the lamp may be good, but your running light filament in the same bulb may not be). I'm almost thinking your lamps are simply out. Unless you've replaced them already and the problem was still present after the replacement. Or maybe your lamp sockets have a problem. You really need to get a cheap DVOM or a 12V test lamp to dig into it further.

 

[WUTANGSUUU]

You may want to get a replacement lamp for your front parking/running lights and see if a new lamp fixes the problem up front. Perhaps do the same for the rear tail lights (your brake light filament in the lamp may be good, but your running light filament in the same bulb may not be). I'm almost thinking your lamps are simply out. Unless you've replaced them already and the problem was still present after the replacement. Or maybe your lamp sockets have a problem. You really need to get a cheap DVOM or a 12V test lamp to dig into it further.

Right. For my front markers, it turned out I just needed to jimmy around the drivers side for it to come back on and I had to replace the passenger side marker bulb.

I replaced the tail light/brake dual filament bulbs, but still no dice.

Back to square one, everything actually works now besides my tail lights. I found my old multimeter, but the BW wire splits and grounds for every single bulb on the harness, so I'm not really sure where to start to find continuity (If that's what I'm looking for).

It seems the light failure sensor box is underneath panel between pillar B and C on my car. I have a feeling that might be the problem.

 

[93celicaconv]

Let's use your old multimeter.

First, I'll assume your rear tail light lamp is an 1157. Is that right?

Remove one of the lamps from it's socket/holder. On the lamp, the two solder-surfaces at the bottom of the bulb are the +12V power connections to the filaments. The bulb bottom silver or brass surface is the bulb's ground. Looking at the socket, the side contact is for the bulb ground. Using your multimeter (set to "Ohms" or "Continuity"), touch one lead to the side contact inside the socket, and the other lead to a body ground source. If you have continuity (you are getting a low ohm reading), then your wiring harness ground wire is properly grounded with no open circuit (meaning it is good). If you get infinite ohms, you have no continuity, meaning you have an open circuit in the wiring harness ground.

Do this first and let's find out what you have for ground continuity back there.

 

[WUTANGSUUU]

Let's use your old multimeter.

First, I'll assume your rear tail light lamp is an 1157. Is that right?

Remove one of the lamps from it's socket/holder. On the lamp, the two solder-surfaces at the bottom of the bulb are the +12V power connections to the filaments. The bulb bottom silver or brass surface is the bulb's ground. Looking at the socket, the side contact is for the bulb ground. Using your multimeter (set to "Ohms" or "Continuity"), touch one lead to the side contact inside the socket, and the other lead to a body ground source. If you have continuity (you are getting a low ohm reading), then your wiring harness ground wire is properly grounded with no open circuit (meaning it is good). If you get infinite ohms, you have no continuity, meaning you have an open circuit in the wiring harness ground.

Do this first and let's find out what you have for ground continuity back there.

0.00 Ohms is the reading I got with my multimeter when I used it on the bulb socket.

 

[93celicaconv]

If that is what you are getting, then you don't have an open in the ground circuit. That's great.

Now, with the same socket you tested, turn your parking lights on (with the switch), turn your old multimeter of VDC, then touch one probe to the same ground point you did above (in the trunk area), and with the other probe, touch each of the two bottom contacts (that would contact each of the two lamp bottom filament contact points), being careful not to touch the side of the lamp socket with the probe when touching a bottom contact. You should get +12VDC on one of the contacts, 0VDC on the other.

Let us know what happens.

 

[WUTANGSUUU]

If that is what you are getting, then you don't have an open in the ground circuit. That's great.

Now, with the same socket you tested, turn your parking lights on (with the switch), turn your old multimeter of VDC, then touch one probe to the same ground point you did above (in the trunk area), and with the other probe, touch each of the two bottom contacts (that would contact each of the two lamp bottom filament contact points), being careful not to touch the side of the lamp socket with the probe when touching a bottom contact. You should get +12VDC on one of the contacts, 0VDC on the other.

Let us know what happens.

I just recovered from being sick, but that's not as important as my brake-through (Pun intended).

Before I got ill, I got carried away and tore open the interior area between the b and c pillar on the driver's side to access the Lamp Failure box that was within.

Upon inspection, the box was fried. Visibly melted on the outer plastic, motherboard confirms a blown jumper wire.

So, I ended up splicing the wires that run to the lamp failure to the wires that run to the taillights and to the front of the vehicle, effectively bypassing the box.

I attached the LIGHT GREEN WITH RED STRIPE wire to the GREEN WITH WHITE STRIPE wire and I attached the LIGHT GREEN NO STRIPE wire to the GREEN NO STRIPE wire.

Bang. I have tail lights once again.

 

[93celicaconv]

Just got back from a couple long trips. Glad you found the problem and figured through a solution that works.