Gauge Cluster Not Lighting Up (just tach and speedo)

[flipture]

First I'd like to say hello to everyone since this is my first post on here. I just picked up a 93 240SX SE a few days ago. I've wanted one for quite some time now and finally have it!!! :-D

It had a couple of problems when I bought it, one being the gauge cluster and dash lights do not light up behind the speedo, tach, and any other back lit button on the dash when the head lights are turned on. The previous owner said that he was installing the head unit and shorted something which blew a couple of fuses. He replaced all of the fuses that were blown and everything that went out came back except for the tach/speedo lights.

I've done a lot of reading and research over the past couple of days so I'm not just asking this question blindly. I've got it sorta narrowed down but don't really know where to go from here.

Here is what I've checked/done so far:1) Read the factory service manual2) Checked fuses (i'm pretty sure the fuse that this runs off of is the second to bottom left, i found that it controls the rest of the lights in the cluster like the low fuel light etc...). Fuses are fine.3) Pulled out the gauge cluster and checked bulbs. The bulbs look fine.4) Checked the connections behind the head unit. Everything looks fine so i don't think he accidentally grounded something wrong back there. I even unplugged it completely and tested to see if he had something funny going on. Still no luck.5) Pulled out the dimmer switch, inspected, and tried to bypass it by bridging the two wires on to make it light up (dont' remember which wires it was exactly but i read a thread on here that pointed out which 2 wires it was...). No luck

Where should I look next?? I'm stumped! I have my volt meeter ready...

Modified by flipture at 10:32 PM 11/8/2006
Modified by flipture at 4:50 AM 11/10/2006

[amolao]

Check the FAQ's for timer control module check out, normally all the dash lights are affected when is damaged by a short in the radio wiring harness. At least you are researching and have multimeter ready, you are doing well grasshopper...

If the module is good, I would check the back of the gauge cluster for bad/burned tracks just in case. Start from the specific lightbulb and track the power all the way from the connetions to the incoming connectors into the cluster...

[flipture]

Sweet!! Thanks for the advice. I had read about the TCM but didn't know what/where it was. I will check this first thing in the morning. I'm pretty proficient with a soldering iron so i should be good to go.

I did check the back of the cluster and didn't see anything out of the ordinary. Everything actually looked really new and clean...

I'll come back and update after I try the TCM...

Thanks again!!

[flipture]

So I checked the white box this morning and couldn't see any visible damage to it. Is there any other way to test it? COUld it still be bad even though i don't see any damage? I tried the thing that the guide said wher eyou ground the blue and yellow (i think that was it...) wire and its supposed to work but it just kept blowing a fuse. I also read that there is a fuse in the dimmer switch. When i took the dimmer switch appart i never saw one, just the light bulb... any more ideas??

If i'm going to start testing it where should i begin and how exactly should i go about it?

[amolao]

Something leads me to believe that you have a problem in your cluster, normally if is the TCM , none of the cluster and HAVC will work. But you check the TCM and at least got that isolated. If you had another cluster to swap it will make things a lot easier. If I was you:

a) Find a copy of the FSM, look for wire diagram (specially the cluster ones) it shows every signal and voltage in and out) and trace your missing voltages. Start from the back of the light socket in the cluster all the way back. OR

b) Leave it alone until I was able to find an extra cluster to swap and troubleshoot from there.

[amolao]

I just checked the wire diagram and I really think the problem is specific to your cluster. Check the wiring and connectors for broken/burned leads,etc in the cluster harness. But the cluster main lightning is wired together, as in all the main light work or they don't....

hope this helps...

[flipture]

S

I just checked the wire diagram and I really think the problem is specific to your cluster. Check the wiring and connectors for broken/burned leads,etc in the cluster harness. But the cluster main lightning is wired together, as in all the main light work or they don't....

hope this helps...

So if one bulb in the main portion of the cluster (3 large bulbs) is burned out then none of the three will work?

[amolao]

No, they will work. They are wire together as in the main illumination voltage coming into the cluster and going to all the lightbulbs. If you loose the illumination voltage somewhere before it gets to the cluster, then none of your lights will work. If you have the Ill. voltage in the cluster ALL your lights "should" work UNLESS there a bad/burned track/wire to that bad specific lighbulb or bad lightbulb...sorry if this confusing...

Tell me something, when you have your headlight switch turned to "parking lights" are you still getting the same problem??

You probably checked this already, but have check the actual lightbulbs to see if they are bad???

[flipture]

No, they will work. They are wire together as in the main illumination voltage coming into the cluster and going to all the lightbulbs. If you loose the illumination voltage somewhere before it gets to the cluster, then none of your lights will work. If you have the Ill. voltage in the cluster ALL your lights "should" work UNLESS there a bad/burned track/wire to that bad specific lighbulb or bad lightbulb...sorry if this confusing...

Tell me something, when you have your headlight switch turned to "parking lights" are you still getting the same problem??

You probably checked this already, but have check the actual lightbulbs to see if they are bad???

Alright, first of all thanks a ton for your help

I just went and pulled the cluster out again. I checked all the lights on it. One big one didn't have continuity and one small one so i went to the store and replaced them. I tried it with those and it still didn't work. I tested continuity between one side of the 3 big lights and the other and it tested fine.

I also tested starting where the ill. wire comes in from the harness as far across the back of the board as i could and everything looked ok. I also found that i am getting power to those bulbs with the lights turned on. It looks like it's a grounding issue somewhere but i have no idea where...

i'm not sure if it'd be worth opening up the cluster or anything or if i can test it all from the back...

I did notice that there were two holes on the far sides that were empty and black taped over. I'm assuming this is just somethign that the american models don't come with or something... However i took two of the bulbs from the bottom ones that are paralell and put them in the side ones since it looked like the side ones were in line with the 3 larger ones... it still didnt work.

and yes i get the same problem with the parking light setting. I've never seen the dash lights come on...

FYI it's all the ligths that come on when you turn the head lights on that are on the dash that don't work. not just the cluster lights...

any more ideas?

[amolao]

Whoa...I read your posting a few times and I thought you said it was only tach and speedo light that were out....dont worry is cool. IF all your lights (dash and cluster) are inop, then is your TCM or in between.

But if you have black tape over the two right bottom lights, thats a very bad sign. Somebody messed with that cluster before. I would buy a used cheap one and play with this one when you are bored.

Those two empty light sockets are used on specific models (engine light, cat temp indicator,etc).I have done work on these before and is not that hard, you sound pretty motivated and willing to get this cluster working.

You are saying that you have voltage going to the lightbulbs, then you are missing ground, and if that's the case you are missing ground in a common point where is affecting ALL of your lights.....check grounds coming from the TCM. We are gonna give hell to this thing until it works!!!!

[amolao]

!

[flipture]

Whoa...I read your posting a few times and I thought you said it was only tach and speedo light that were out....dont worry is cool. IF all your lights (dash and cluster) are inop, then is your TCM or in between.

But if you have black tape over the two right bottom lights, thats a very bad sign. Somebody messed with that cluster before. I would buy a used cheap one and play with this one when you are bored.

Those two empty light sockets are used on specific models (engine light, cat temp indicator,etc).I have done work on these before and is not that hard, you sound pretty motivated and willing to get this cluster working.

You are saying that you have voltage going to the lightbulbs, then you are missing ground, and if that's the case you are missing ground in a common point where is affecting ALL of your lights.....check grounds coming from the TCM. We are gonna give hell to this thing until it works!!!!

Well we're making progress . That diagram will help a lot. I'm pretty convinced like you said that it's not in the cluster any more... Although the TCM *looked* fine, i think that still might be the culprit. I've gotta find out which wire coming out of it is the ground (black i'm assuming) and test that.

I have a friend that has a couple extra 240's that he uses for parts so if i don't get this figured out by friday i'm going to go over there and get his help and try another cluster and swap out the TCM...

Any way i can bypass the tcm or something? Maybe try to ground something out from the TCM to see if that is the problem? Can you explain what it does exactly too??

And yes i am very motivated to get this fixed i like a challenge... i learn a lot

[flipture]

Well we're making progress . That diagram will help a lot. I'm pretty convinced like you said that it's not in the cluster any more... Although the TCM *looked* fine, i think that still might be the culprit. I've gotta find out which wire coming out of it is the ground (black i'm assuming) and test that.

I have a friend that has a couple extra 240's that he uses for parts so if i don't get this figured out by friday i'm going to go over there and get his help and try another cluster and swap out the TCM...

Any way i can bypass the tcm or something? Maybe try to ground something out from the TCM to see if that is the problem? Can you explain what it does exactly too??

And yes i am very motivated to get this fixed i like a challenge... i learn a lot

This morning I tested the harness for the TCM as directed by the factory service manual. I followed the directions and according to it, the TCM was bad.

I went to the junk yard and picked up a TCM off of another 240 and replaced mine but the dash lights STILL don't work...

I pulled the gauge cluster inside and i think i'm going to take it appart to see if theres something burned up inside. I have no idea what else it could be unless there is something worng with this TCm i got from the junk yard as well...

Ideas? How can i test to see if everything inside the cluster is ok?

[amolao]

The illumination path begins at the light switch, from them goes to the TCU or TCM where is regulate by the dimmer switch and from there to all lamp circuits...including radio, dash,etc....

Think of the TCU as the local electric company, it manages,regulates and provides the path of light....without it there will no lights. Even though, the actual illumination comes from the light switch, the TCU is the component that "applies" the right signal and voltages for you to be able to see your dash and cluster at night.

The illumination path is kind of complicated, it works in a loop principle. You break the loop anywhere and you have no lights. The TCU is the main item in the loop.

Bottomline:

Check all fuses again.Swap the TCU, is fairly easy and a quick test.Pin 6 of TCU is input and 11 is output. From there it goes to all lamp circuits.

[flipture]

The illumination path begins at the light switch, from them goes to the TCU or TCM where is regulate by the dimmer switch and from there to all lamp circuits...including radio, dash,etc....

Think of the TCU as the local electric company, it manages,regulates and provides the path of light....without it there will no lights. Even though, the actual illumination comes from the light switch, the TCU is the component that "applies" the right signal and voltages for you to be able to see your dash and cluster at night.

The illumination path is kind of complicated, it works in a loop principle. You break the loop anywhere and you have no lights. The TCU is the main item in the loop.

Bottomline:

Check all fuses again.Swap the TCU, is fairly easy and a quick test.Pin 6 of TCU is input and 11 is output. From there it goes to all lamp circuits.

Ok, that makes sence... Since i changed out the tcu (might still be bad so i'll try another one friday when i get to my buddys, they have a couple junk 240's) and it still doesn't work, is there a way i can maybe try starting in the light cluster from where it goes in and grounding it light by light to try to find out where the break is and if it's even in the cluster? My buddy also has some clusters we're going to try but i'd like to get it figured out before friday...

basically i'm trying to figure out a way to send the light circut power (12v i'm guessing) so i can proove if it is or is not the TCM... Is this possible? like could i just bridge one of the positive 12v pins that goes to the tcm and send it to the pin that is illumination?

[amolao]

With ignition/key off and light switch ON check between pin 6 and 15, make sure you have the pins right, see the FSM layout if not sure. Pin 6 should have 12 volts and 15 is ground. Positive lead on pin 6 and negative lead on 15. You will be checking for these from behind the connector with everything hooked up IF...

you have 12V, then you have the right output coming from your TCU. IF NOT...Then check the harness between light switch and TCU. One thing maybe also you will need to check is the light switch, if is your light switch this will be a first one.....Maybe the short created during the installation of the radio was significant enough to damage the terminals in the light switch.... ,and also make sure you dimmer switch is all the way up.....

99% of the time is the TCU. But you never know. But by trying another TCU I think we can say the problem is somewhere else.

[ricebike]

side step: did you also make sure that the aftermarket head unit wires are correctly matched up? it should also have a separate ground wire to the chassis... & the illumination wires should be untapped/ taped off...

[flipture]

side step: did you also make sure that the aftermarket head unit wires are correctly matched up? it should also have a separate ground wire to the chassis... & the illumination wires should be untapped/ taped off...

I did check the head unit, the guy who hooked it up had the ground wire grounding to the back of the head unit which was making it ground through the antenna... i changed it so that it is being grounded off one of the bolts that holds down the shifter...

and yes both of the illumination wires are taped off...

[flipture]

With ignition/key off and light switch ON check between pin 6 and 15, make sure you have the pins right, see the FSM layout if not sure. Pin 6 should have 12 volts and 15 is ground. Positive lead on pin 6 and negative lead on 15. You will be checking for these from behind the connector with everything hooked up IF...

you have 12V, then you have the right output coming from your TCU. IF NOT...Then check the harness between light switch and TCU. One thing maybe also you will need to check is the light switch, if is your light switch this will be a first one.....Maybe the short created during the installation of the radio was significant enough to damage the terminals in the light switch.... ,and also make sure you dimmer switch is all the way up.....

99% of the time is the TCU. But you never know. But by trying another TCU I think we can say the problem is somewhere else.

Ok when i tested thsi morning i tested with the TCU *NOT* hooked up... maybe this was my mistake. I will re-test with it hooked up and see if i get the correct voltage. I seriously doubt its the switch since if it was a significant enough short to melt that it would have smelled and the guy that shorted it said that it didn't make any kind of smell... i won't rule it out quite yet tho...

Once again thanks for all the help and i'll get back to you guys ...

[flipture]

Ok i found on the back of the cluster that one of the resistors in line with the illumination circut is showing no continuity. There are two, they both go from the bottom contact, one goes to top left and one goes to top right. they look the same but the one the left has no continuity, the one on the right does. I'm thinking this could be a problem... Here's a picture with the one that i'm talking about circled...

Could this be my problem?

Also notice the missing bulbs... i don't think those would be a problem since they look like theyre run parallel but not sure...


Modified by flipture at 6:56 PM 11/8/2006

[amolao]

They are diodes, my friend....not resistors. Check this link:zerothread?id=96108

This one the first time I had problems with a cluster, I had bad DIODES on mine, and it shows how to test them and the symptoms I had back them. Yes, those diodes are in your illumination path but if they go bad they will affect your car in a different way.

Lightbulbs are hooked in parallel, if one goes bad, the other will continue working, for safety reasons. You can pull your cluster off your dash and your car will run fine, again for safety reasons. If you were to suffer a catastrophic failure in your cluster while driving, your car will continue running somewhat safe and without problems.

[flipture]

They are diodes, my friend....not resistors. Check this link:zerothread?id=96108

This one the first time I had problems with a cluster, I had bad DIODES on mine, and it shows how to test them and the symptoms I had back them. Yes, those diodes are in your illumination path but if they go bad they will affect your car in a different way.

Lightbulbs are hooked in parallel, if one goes bad, the other will continue working, for safety reasons. You can pull your cluster off your dash and your car will run fine, again for safety reasons. If you were to suffer a catastrophic failure in your cluster while driving, your car will continue running somewhat safe and without problems.

Well i'm not seeing the strange problems like you mentioned. They just simply don't turn on. I tested one diode and it had continuity, and the other did not but i only tested in one direction. I will try both this time. I just read through your thread so now i think i have a better idea on how to test them...

And yeah, i found out that the car runs just fine without the cluster . Just make sure you've got enough gas before you try it .

Tomorrow i'm supposed to meet up with a friend to test a good cluster so I should have a good answer tomorrow... If i find that the cluster was the weak link I'll test and find exactly what was wrong and report back on how to fix it...

Could you explain to me the process of testing the two diodes on the back and what i should expect to see if it's good or bad? Also what settings to use on the meter?

[amolao]

The basic rule is to check them one way and you get an open reading (high resistance) on your meter, reverse the leads, check and you should have a short reading (0 or almost zero resistance) on the meter. You test one diode at a time, this is the basic test. If you like to get into more details like how diodes work there are some very good guides on the web.

You should get a good indication of any questionables diodes. To make sure and if you are good on soldering, unsolder the diodes and conduct the test for a better result and to make sure. If the diode checks out high or low BOTH ways then is a bad diode. Maybe you have the diode test setting on your meter, if not, use the ohms setting. If you desoldered the diodes BE very careful with the heat on the flexi board or you will ruin the circuit......

[flipture]

It looks like i've figured out what the problem is. Yesterday I went through the cluster and tested each of the wires with it plugged in. Everything looked good except for the ground for the Illumination so i bridged it with another wire and gave it a direct body ground and the cluster lit up!! Now i just have to trace that ground (the RED wire with the YELLOW stripe) to where it is faulty. I guess I'll start at the ECU and see if it goes all the way there... If not, I'll just use the FSU to follow it from the back of the head unit all the way down...
Modified by flipture at 1:43 PM 11/13/2006

[amolao]

Cool, Im proud of you. Make sure to post the closing results and pics if possible. That way others benefit from this, this is a common problem among 240sx owners.

[flipture]

Ok, I traced the RED/YELLOW wire from the cluster to the dimmer switch. I manually grounded that wire and the lights worked again but they still did not work with the dimmer. Then i looked at the TCU (yes the new one i bought at the junk yard) and saw that there was also a RED/YELLOW wire coming into it that had continuity from the cluster to the TCU. When i grounded that one the cluster lights came on again but this time the dimmer switch worked!!

I opened up the new tcu (new from junkyard atleast) and found the problem with this one right away. One of the tracks on the circut was burned up. I simply borrowed the wire from one end of a resistor and bridged the track. When i plugged it up it worked like new!!

I still have a couple of questions and want to clarify some things so i'm more clear on how the whole thing works...

When i would test continuity between the red and yellow wire and a chasis ground i would get 0.00 resistance which tells me that it's grounded. This baffles me since if i would connect it directly to a chassis ground manually it magically worked!! Why would it test OK for ground but at the same time, grounding it out from the same spot would make the lights work?

I'll take pics of the repaired TCU in a bit and post them if anyone doesn't quite get what i did and so you can see what a burned track on a circuit board looks like.