QuestionQUESTION: Our 1998 Chrysler T/C 3.8L LXi stopped running. Towed it to dealer and had to replace the PCM. Problem fixed but now the instrument panel lights don't come on when headlights are on at night. Is this problem in any way related to the PCM repair? What is needed to repair this issue? After very $$ PCM repair, not looking for another $$ repair. Was hoping that the dealer will fix due to problem being related to their replacement of the PCM. Instrument panel lights worked just fine prior to PCM issue.
ANSWER: Hi Pat,
The panel lights are mediated through the body computer, not the pcm. But before going any further I wonder if you might not try rotating the knob on the headlamp switch to see if by accident it might not be turned all the way down as to instrument cluster brightness? If not, let me know and I can tell you where to check the circuity.
Roland
Thanks for quick response. I had already tried rotating the headlight switch to all of the positions and moved the dimmer thumb-wheel to be sure it wasn't completely dimmed. I should've mentioned that before. I also should've mentioned that the dealer removed the ignition and installed a different iginiton for testing purposes before they determined that it was the PCM. They then reinstalled the original iginition switch(steering column). They mentioned that they would have to removed the dashboard to perform diagnostics on this problem. Any suggestions that I could try to troubleshoot would be most helpful. I understood your explanation about the pcm not being related to the instrument panel lighting, but could something else have happened during their troubleshooting/removal & reinstallation of the ignition switch that could've caused this lighting failure? It just seems too coincidental not to be related.
Hi Pat,
If all the other dimmable panel/switch lights in the cabin are working, then the issue is not related to the body computer or the headlamp switch/dimmer but rather has to be a cold solder joint at the cluster plug/printed circuit board interface. Pin 6 is where the variable voltage comes in for lights, and pin 13 is the ground return point. You would remove the cluster and reheat the solder joints with a soldering pencil.
If all the inerior dimmable lights are out, then the problem is likely in the headlamp switch's variable resistor or the wire that comes to it from the body controller (pin 8).
Let me know what you find out, or if you have further questions.
Roland
---------- FOLLOW-UP ----------
QUESTION: Thanks again for the insight. I'll definitely give it a shot. Where is the cluster plug located and how accessible is it to remove and resolder? Is it easy to identify and remove for repair? I apologize for this next question. It's my wife who the dealership was dealing with as the minivan is her vehicle. Could this failure been staged to take advantage? Could a wire have been purposefully loosened or cut where this cluster is located? I'm still having trouble with the incredible coincidence of this failure.
AnswerHi Pat,
My working theory is that it is the cluster itself that is at fault, which cannot be easily disturbed except perhaps by flexing the instrument panel as a whole. This theory assumes that the other dimmable lights and switch illuminations all across the front panel are still working and that it is only the cluster lights that are "out". You didn't tell me whether this is the case or not.
If all the dimmables are "out", then the wire from the dimmer rheostat to the body computer or to ground might have been broken/disturbed, which could occur in the service process. So that is the pivotal issue about the coincidence.
You would have to remove the instrument cluster to resolder the plug-socket/circuit board interface. Because of the several steps and a few drawings that may be helpful in the processs, I would prefer to xerox copy and postal mail you the pages. Use the "thank/rate" tab to enter your address in the comments section.
Roland
Because some lights don't work and some don't dim, there has to be some problems with the wiring in and around those plugs or the circuits that they supply.
-----Original Message-----
From: Roland Finston
Sent: Sep 4, 2008 12:55 PM
To: prondo@earthlink.net
Subject:
Hi Pat,
If the dimmer switch still causes other lights in the interior to vary in intensity, then the problem has to be in the instrument cluster itself. That is the bottom line. So check that out and let me know if that seems to be the case, and if so whether I should copy the pages and mail them to you, by postal mail.
Roland
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Date: Thu, 4 Sep 2008 19:26:26 -0400
From: prondo@earthlink.net
To: rfinston@hotmail.com
Subject: Re:
O.K. The dimmer thumbwheel does not dim any interior lights. However, the interior lights(gear indicator,mileage,radio,outside temperature display) flicker while moving the thumbwheel but the lights remain full bright when the thumbwheel is no longer being moved no matter where the thumbwheel position is when I stop. All interior lights are working(gear indicator,mileage,radio,outside temperature display......) except the instrument panel(temp gauge, tachometer, speedometer and fuel gage) lights. I'm not sure if that means that this problem can still be service related or not. I'm just struggling with the "unfortunate coincidence" of the failure. At this point, explain what this means and how I would proceed for repair. If this can be service related, I might ask for your help in phrasing what I need to say to the dealership. Your help is greatly appreciated.
Hi Pat,
I have a new theory that does relate the dash lights to the ignition switch replacement! and thus to the repair done at the shop. I noticed that the ground path from the cluster lights to ground is shared by the key-in ignition switch (the switch that warns you that you need to remove the key if you open a door). If that wire were actually attached to 12V instead of to the key-in sense circuit (due to a short in its wiring) the dash lights would have 12V on both sides and therefor not produce any light.
The pins at the under dash fuse box (junction box)for the cluster lights are on the black 36-pin plug. The variable voltage wire for the cluster and the a/c panel lights is on pin 1 (2 orange color wires). The return ground wire (2 black wires) is on pin 28. If you will measure the voltage on those two wires that will give you part of the answer (insert a pin through the insulation to reach the internal conductor). Pin 1 should show a variable voltage when the headlights are "on" as you move the dimmer control. Pin 28 should show 0V and also it should show 0 ohm to ground. If this proves to be OK then that is not the problem and the answer is that the path from pin 1 (on one of the orange wires of pin 1 that goes to the cluster bulbS) is "open", probably due to a break in the solder joint at the cluster socket (pin 6 or pin 13). This is my alternate theory. Unfortunately because of the two orange wires on pin 1 you can't verify this unless you go to the a/c panel and unplug its two plugs because its bulbs are also in parallel with the cluster bulbs. Then you could see what the resistance is between pin 1 and pin 28 of the black plug. An infinite resistance mean an open in the circuit to the bulbs, a few dozen ohms means the cluster circuit is OK, and 0 ohms means a short in the circuit. I notice one problem: there is a discrepency in the pin number assignment; on one drawing the pin for the cluster/ac lights is shown as 1, on another page it is shown on pin 8 so you may have to do all these measurement twice!
That is my analysis. You can decide what to do about the situation. I would be inclined to tell the shop that it appears they were in some way involved because of their having changed the ignition switch.
Roland
