Tail and Dash Lights- not a fuse?

A couple weeks ago I noticed my dash lights didn’t work. Then I noticed my tail lights were out too. Brake lights, blinkers, and headlights work fine. I checked the TAIL fuse and relay, both looked fine but I replaced them for good measure. The issue is still there. I am unsure if the rear plate light work or not, I will check later because I am out of town.


I am still learning about cars and making some silly mistakes, so here are some things to consider that may help:

1. I’m not the original owner, I’ve had it 6mo and have had a few strange electrical issues before. Examples are certain lights/window not working unless they’re tapped.
2. Before the dash/tail issue, headlights used to shut off on their own after I turned off and locked the truck. Now, headlights remain on unless manually shut off.
3. Stereo, speakers, and alarm system are after market, but were installed by a professional months before this issue began.
4. A few weeks before the issue, I accidentally forgot to tighten the battery hold down and it caused the ground cable to tear off of the truck’s frame. The issue came just a week after I reattached the cable.

Please give me your suggestions... I drive to work in the dark and don’t leave my office until dark so this is a real issue. Thank you.

 

Only guessing, but both are controlled by Body ECU. You may check all connectors around JB/1 (the big box where in cabin fuses are)

 

Can you elaborate a bit more? Not sure where the body ECU is or what I should check for.

 

I'm sorry for the "shortcut". The BODY ECU is controlling some functions of the "body " of the truck. Some are like a key in the ignition ding, seat belt reminder ding, switching off headlights after you leave the car, dimming in interior lights after you settle in, chirp horn after remote locking, door locking, windows operation etc. In 95 models it started as an "Integration relay" annoying "key in the ignition ding", "lights on buzzer" and "click it or ticket" ding. Now in more modern cars the Body ECU does much even more automation and checks. That's like frickem Mission Control in Huston.

Anyway 1st Gen Tacoma has the BODY ECU integrated with JB/1 - the big junction box under the dash on the left side (where the cabin fuses are). There are whole bunch of plugs and wires going in there.




Internal guts of Body ECU and logic is not published (similar to other ECUs in truck) so it is difficult to find what's wrong. Try to knock on the plastic box or wiggle wires behind - it may help or may notit.




The worse case scenario is that the electronic board in the box is going bad, but may be also some old connectors got loose or rusted. This is really hard to tell, and I am very happy that my 95 has so much simpler logic - so much less to go wrong.

 

Have you checked the bulbs ??

Simple things first

Front marker lights on??

For the dash lights has the rheostat failed or been turned down so the lights are off.

 

hope this helps

 

So I noticed some things thanks to all of your suggestions. I confirmed that the license plate lights do not light up either, which convinces me that I can find the root of the problem through the fuse. I swapped the fuse and used a circuit tester- there is no current running through the fuse. Now it’s just a game of identifying the root problem.

I noticed that i have exposed wiring underneath my truck, and around the hitch.



There is also a green wire running underneath, near the spare:




I'm assuming this is not stock, considering it is zip tied? Looks like it is probably for tailgates. Not sure if maybe all this wiring being exposed maybe caused the problem.. please let me know what your thoughts are it is much appreciated!

 

Thank you for this. I just printed it out, I know this is going to come in handy.

 

The wiring you are seeing is for trailer wiring, green wire goes over to the pass. tail light for that sides turn signal, you should see three others go up to the drivers tail light area (turn signal, brakes and parking light, and the white will be a ground. There should also be a box where five wires go in, four come out going to the four flat plug for the trailer.

 

Thank you, I need to make sure everything is connected somewhere and that it is functioning. Is there a way to test the end that goes into a trailer, without using a trailer?

 

Also, in the event that I were to give up on solving this myself, who would you all recommend that I take my truck to? An ordinary mechanic, an electrician of some sort, a Toyota dealership?

 

Did you check for voltage at the fuse with the taillight switch on? Follow the wiring diagram and check that you have battery power at the terminals of the fuse and relay that should have power. Some terminals should have 12v all the time, some only when the switch is on.

If the fuse isn't blown and the dash lights don't work then I highly doubt it's a problem with the wiring at the rear. If it were a problem back there it would either short out and blow the fuse or it would be a disconnected wire (like a ground) preventing the taillights from working, but in that case the dash lights would still work. Follow my logic? See the wiring diagram, the rear lights circuit and dash lights circuit split right after the TAIL fuse. That's why I say verify voltages at the fuse and relay first.

 

Yes I understand. The problem is clearly occurring before the fuse, because there is no current coming to the fuse at all. I checked with the light switch on and off, and used multiple fuses but no luck.

I don’t really know how to check if the relay is working, I bought a new one and that didn’t do anything, so I assume it is working. Could it be a problem with the body ECU, or the light switch itself? Or perhaps just a bad connection at the fuse panel?

I keep hearing that bad ground could be a problem, but I have a hard time visualizing/understating this. I’m not sure where a ground occurs or where it is needed, therefore I don’t know how to check for ground.

 

Current is different than voltage. I'm not sure if you are just being sloppy with words.

If the wire were broken after the fuse you wouldn't have any current going through the fuse because there wouldn't be a complete circuit back to ground, but you'd still have voltage measured at the fuse terminal (1 probe on fuse terminal, 1 probe on battery negative)

And of course if the tail and dash lights aren't working then you already know there is no current draw.

By measuring for voltage you are trying to find where the circuit is broken. It sounds like you don't have voltage at the TAIL fuse, so then you move one step closer to the battery and see if you have voltage at the relay terminals. If not then you go back to the big fusible link and check for voltage.

 

That makes sense. How do you test at the relay terminal while it is plugged in? I replaced the relay entirely, so do I test the area where it is being plugged in?

 

You unplug the relay then check the terminal in each hole. One probe on the terminal the other probe on battery negative with the multimeter set to DC voltage.

If you look at the wiring diagram, two of the terminals should have 12+ volts (even with key off and light switch off). There might be a little diagram printed on the relay that you can match to the wiring diagram to see which terminals those will be. The other 2 terminals should have 0 volts.

 

If you were close I would be glad to help .

Hang in there take one step at a time you will figure it out

 

Had this same issue before. It was the trailer "splitter" box which is connected to one of the tail lights. I took out both tail light assemblies and removed the box and plugged in the connector to the tail light as it was before adding the trailer wireing . Problem fixed. There is a great deal of discussion about this situation. Think it is pretty common for those boxes to fail in that mode after a time.

 

In your case the TAIL fuse was blown from a short related to the trailer splitter box. The OP claims his TAIL fuse is good. If his TAIL fuse is actually blown then the rear wiring is the most likely problem area.

https://www.tacomaworld.com/threads/dash-lights-went-out.425949/

 

Precisely why I was bringing up the trailer wiring, but you’re right. Since I do not have a short, the problem probably lies somewhere in between the body ECU and TAIL fuse. Or, a grounding problem perhaps.

Unfortunately, it gets very difficult to work on your truck when you work from dark to dark. Hopefully now that the weekend is here I’ll catch up on it. Please keep the suggestions coming, I can feel myself getting closer...