Partial non-working instrument cluster lights

QuestionEdit

QUESTION: Hi I own a 2004 300m special, my instrument cluster (speedometer, gas, temp, etc.) lights don't light up at night when you turn the headlights on most of the time and then they light up sometimes like normal all other lights work fine Thank you Bo.

ANSWER: Hi Bo, Are you speaking only of the variable brighness level illumination lights, or do you also mean the gauge readings/numbers don't illuminate? Warning lights are all ok when this happens? Let me know and I'll go from there. Roland

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QUESTION: Hi Roland No lighting (illumination) at all, don't know about the warning lights (did not come on or any warning, same power circuit ??) can't drive at night with no instrumentation lights. Wiring diagram or schematic would be great. Thanks again Bo

ANSWER: Hi Bo, It appears to me as I read over the wiring diagram for the cluster that the illumination level of the panel lights is controlled digitally on a wire that also brings the data for all the readings of the instruments, there is no identifiable lighting level wire. So if the rest of the dash board's variable illumination levels are working there must be something internal to the cluster that is causing this intermittent situation. When it happens, try to see if all the gauges also go out or are still operating normally, because it could be an intermittent connection of that digital data wire that comes from the body computer. If the entire dash light variable compliment goes out, then that is an issue with the connection from the headlamp switch to the body computer and we can deal with that. Please 'rate' my answer (see below). Thanks, Roland

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QUESTION: Roland Is there a power source for these lights??. By all the gauges going out do you mean just infront of the steering wheel, yes they are all out. When the cluster lights went out I would turn the headlamp switch on and off several times the brightness switch and turn the engine off wait a few min back on and no results. Thanks Bo

AnswerEdit

Hi Bo, There are 4 fuses that supply the cluster, all in the junction block behind the left end cap of the dash: #1,4,7,19. So perhaps one of those has a subtle crack in its wire that is opening up spontaneously and then closing as it cools down. There is no cluster illumination bulbs shown in the diagrams so that is why I conclude that the levels are controlled digitally from the body computer. But on the other hand, if the gauge readings disappear along with the illumination then that could be an issue with digital connection wire but also it could still be a flaky fuse. However, if that wire were bad, then while driving in the daytime I would expect the gauges would go out in the same way as the lighting did at night. Variable intensity dash lights are designated as 'E2' wires when there is a dedicated supply line for the bulbs in the cluster, but there is no such wire shown, nor are the illumination bulbs shown in the wiring diagrams which is why I conclude that they are powered from one of the four fuses I listed and controlled digitally as to their intensity. The cluster will do a self-test if you press and hold the trip reset button, then turn the key from lock to unlock and release the button. There is no description of all the steps it will go through, unfortunately.