No lights on EATC and Radio....time to fix the prob...HELP

CaifanSC

SCCoA Member
Since i got my 94sc the lights on the EATC didnt work (the display does, but not the knob illumination) but i really didnt worry about it. Today i installed a factory single CD unit instead of the aftermarket unit and the buttons dont light up either. In addition, the clock works fine when the lights are off (nice and bright) but when the lights are on its very dim....this is ok when its complete night time, but not when its dusk and there's still light...you just cant see the clock during those times. I have replaced the clock with 3 others and it does the same. I have also replaced the EATC unit with a different one and it works the same way...full operation of the module and the display, but no illumination.

The odd thing is that the aftermarket radio I had was fully illuminated (all buttons) and the display too, but the display went on and off sometimes. But now that i replaced the factory radio...none of the lights are on except for the display...so the problem MUST be fixed now. Im stumped, the clock, radio, and EATC illumination all are under the same fuse, and that fuse is good, and the rest of the items on that fuse work properly (rear def. switch, cluster lights...cant really test the rest: phone switch & automatic shifter lamp because i dont have those).

Any thoughts? anybody have similar problems? What can i check? Thanx fellows
 
Do the instrument cluster lights dim and brighten when you rotate the headlight switch knob?
 
I don't know if the illumination for a 94 is the same as 89-93.
One thing I wouldn't assume is that there is only one fuse for illuminating all these instruments. For example, the instrument illumination on 89-93 models uses two fuses, #14 and #17.
 
The fuse panel is set up differently thats for sure.....instead of numbers like on the early models, the 94+ fuse panels are organized by names like "cigar ltr" for the fuse that controls the lighter, "cluster" for the fuse that controls the gauges, abs lights, air bag lights, chime, autolamp sensor. For the one im interested in called "Panel Lps." they have all that stuff listed.

Like i said, its kinda weird b/c the rest of the things in the same fuse work properly...i forgot to include that the ashtray light is also in the same fuse and it works. Im also gonna test the automatic shifter light. The plug for the lamp is there and me, being the parts whore that I am, have one of those...so im gonna test it out just to make sure it works and its not shorting out or something.
 
I think you'd be able to solve the problem easily if you have the Electrical Troubleshooting Manual (EVTM). It's possible that you have a relay for the knob illumination (similar to the LCD illumination relay in 89-93 models).
 
Haha, i sort of beat u to it....i slapped out my EVTM and started checking things out. So far im having a hell of a time getting the right circuits/wire colors/circuit #'s straight because of all the mis-matched info between teh shop manual and the EVTM. I think im going to gether some info and start testing things.

What im thinking is that, since all the other accesoreis work, there is something going on in the harness that brings the light power to those three accesories...since they are so close.
 
I don't trust the EVTM very much, I have found too many errors in it. What I go by is the actual fold out schematic.

In the lighting I found that the backlighting bulbs in the HVAC control head have an effect on the digital display. Apparently the bulbs are used as some sort of biasing resistors for the chip that controls the dimming of the VF display.

My digital display was out, so I disassembled it to find that both backlighting bulbs were burned out. I replaced them and the digital dispaly came back. I have fixed a couple others this way as well.

On the radio there may be a similar problem with backlighting bulbs. If the dimming circuit is connected to the radio (meaning someone who put the aftermarket deck in didn't pull it out of the connector or something) I'd take the radio apart and look for backlighting bulbs.

On the clock, I don't know. Fix the other stuff first and see if the clock comes back. A lot of things seem to influence one another on the dimming circuit.
 
Yea, im getting discouraged at these manuals...there's way too many errors. As far as the bulbs, i checked them and they lit up. I did this on both EATC units i had, and swapped them both and no cigar. As far as the radio goes, im going to try to see if its easy to pop open. I've never taken a radio appart...but hey, there's a first time for everything.
 
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