Instrument Cluster Lights Went Out????

[ChrisKringle]

They do not work, the speedo/tack area, plus climate control area. I checked number 18 fuse after doing a search, ok. The lights just went out last night, at first they were dim and flickering, then just out, anyone have an idea?

 

[JLandry]

Questions:



Is the entire instrument cluster not illuminating, or just the speedometer and tachometer?



Are any other areas of the dash (radio, courtesy lamps, etc. ) not illuminating?



Have you tried fiddling with the dimmer rheostat in the headlight switch on the dash?



I'm inclined to think there might be something wrong with the headlight / dimmer control switch. It has a separate module (switch) inside which controls interior lighting. The rheostat signal is referenced by instrument cluster to control illumination intensity of interior lighting. The headlight switch and rheostat don't control the interior lighting directly... the instrument cluster does this. The headlight switch and rheostat only tell the instrument cluster what to do.



Something you might want to try before considering replacement of the headlight switch is an instrument cluster self-diagnostic test. The instrument cluster self-test checks circuit continuity between the headlight switch and the instrument cluster.





Get a pad of paper and pencil ready.

With the ignition switch turned OFF, press and HOLD the odometer reset button down.

Then while still holding the odometer reset button, turn the ignition switch to the RUN position, but do not start the engine.

Release the odometer reset button.



The instrument cluster will go through a series of tests and illuminate all the segments of the odometer window. Following these tests, if any faults are found, the odometer window will display a fault code consisting of a "C" followed by two digits. You'll have 3 seconds to write down each fault. If no faults are found, or at the end of the fault code list, two pairs of zeros will be displayed like this: "00 00". Post any fault codes here and we can tell you what they are.



Good luck,



John L.

 

[ChrisKringle]

Here are the codes it displayed:



26 04

A4 41

A7 12

AA 12



Every time I re-do the diagnostic test it gives me slightly different numbers, for instance A7 12 and AA 12 turned to A7 15 and AA15 the next time I tested it.



Here's what it gave me when I just tested again:



26 11, A4 48, A7 19, AA 19



Only the gauges (speedo, tach, volt, temp, fuel) and climate controls in center of dash went out. It's the same lights which respond to the dimmer, as if I turned it down.



The radio works (aftermarket though), the overhead with temp/milage works and dims, the odometer and gear selector works and dims, the seat heater indicators work, I don't think the light switch is working/dimming either.

 

[JLandry]

Well I can't see anything jumping out from the instrument cluster self-test results that suggests a problem. Interestingly, most of those codes aren't even listed in the Service Manual, so I'm not sure what's up with that.



If some of the dash components are illuminating and dimming, that would seem to eliminate the headlight switch and rheostat as being faulty, because the instrument cluster only gets one lighting and one dimming signal from the headlight switch, and it's used for used for everything.



A long shot, but have you checked fuse number 22 in the Integrated Power Module? According to the wiring diagrams in the Service Manual, fuses 18 and 22 supply power to the instrument cluster.



Failing that, the symptoms seem to be pointing to a problem internal to the instrument cluster. BTW, the instrument cluster also supplies power to the lamp in the headlight switch (not the switch itself), so even that points back to the instrument cluster. I hope it's not the instrument cluster because your looking at about $500 retail at the dealer.



This problem might necessitate a trip to a dealer who can use a DRBIII scan tool to observe the inputs and outputs to the instrument cluster while activating the headlight switch and dimmer rheostat.



Best of luck to you,



John L.

 

[ChrisKringle]

So if I replace the instrument cluster with a used one, does it display the mileage from the donor truck, or is that info still displayed from my truck computer?

 

[JLandry]

So if I replace the instrument cluster with a used one, does it display the mileage from the donor truck, or is that info still displayed from my truck computer?

This quote from the service manual should answer your question:

CAUTION: Instrument clusters used in this model

automatically configure themselves for compatibility

with the features and optional equipment in the

vehicle in which they are initially installed. The

instrument cluster is programmed to do this by

embedding the Vehicle Identification Number (VIN)

and other information critical to proper cluster

operation into electronic memory. This embedded

information is learned through electronic messages

received from other electronic modules in the vehicle

over the Programmable Communications Interface

(PCI) data bus, and through certain hard wired

inputs received when the cluster is connected to

the vehicle electrically. Once configured, the instrument

cluster memory may be irreparably damaged

and certain irreversible configuration errors may

occur if the cluster is connected electrically to

another vehicle; or, if an electronic module from

another vehicle is connected that provides data to

the instrument cluster (including odometer values)

that conflicts with that which was previously

learned and stored. Therefore, the practice of

exchanging (swapping) instrument clusters and

other electronic modules in this vehicle with those

removed from another vehicle must always be

avoided. Failure to observe this caution may result

in instrument cluster damage, which is not reimbursable

under the terms of the product warranty.

Service replacement instrument clusters are provided

with the correct VIN, and the certified odometer

and engine hours values embedded into cluster

memory, but will otherwise be automatically configured

for compatibility with the features and optional

equipment in the vehicle in which they are initially

installed. ​