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Dash Lights & Clock

24 August 2006
Jupiter, Florida
Its been quite a while since I posted here but I ran into an issue that merits some input. Here is the situation: A 1991 with 87,500 original miles, mechanically and cosmetically very well cared for. The car has been sitting covered in the garage:confused2:. I've started it twice a month and put maybe twenty five miles on it at each startup. I've changed the oil and opened/closed all doors and hatches regularly. The battery has been on a float charger. The climate control has been run at each startup. Steering wheel rotated, car rocked back & forth in 1st/reverse if allowed to sit for more than two weeks. Fuel tank drained once and stabilizer installed afterwards. When it was parked and at each startup, every light/function & gauge was working and within the factory manual spec allowance. I.E. everything worked.

Some additional background info: I installed a new head unit (Alpine), amp (JL), speakers (Alpine) & SW (JL) 4 years ago. I ran a #4 positive cable directly from the battery through the front firewall and tunnel. The amp sits behind the driver's seat against the firewall. The amp remote turn on is wired into the head unit. The head unit is wired into the ignition ACC (same as factory radio). The head unit illumination wire is in parallel with the ACC power wire (The head unit is illuminated when the key is on and NOT dependent on the vehicle illumination control).

Upon starting it this past Saturday, the dash lights and the clock would not illuminate (although all the cluster lights functioned properly). The headlights work properly, interior courtesy lights function properly, all other lights and functions work properly. I checked each fuse under the hood and next to the drivers foot well: all fuses were good. I replaced the 7.5 amp clock fuse just to be sure but to no avail. I rotated the dimmer pot on the dash (left side of steering wheel) several times and sprayed it with deoxit (through the annular space around the knob), still to no avail. I checked the voltage across the 7.5 amp fuse holder terminals (13.8 volts when engine running). All other lights and functions work properly. I've glanced through the manual several times and searched several of the forums but have not come away with any insight as to what else to look for. Any suggestions?
The dash light brightness control unit and the dash lights (and a bunch of other stuff) get power via the taillight relay. The easiest way to check that this supply is OK is to open the glovebox and check to make sure that light comes on. If the glove box light does not operate, then turn the headlights on and make sure both taillights are operational. If the right taillight is out, check the #38 15A fuse. The #38 fuse supplies the dash dimmer circuit, the clock, glovebox as well at the tail and side marker lights

According to the 1991 wiring diagram, the clock is not on the dimmer circuit; but, both are on the #38 fuse which is why I suggest it as the first place to look.

If the glove box light works, then check the power window switch lights or power door mirror switch lights. These are also on the dimmer circuit. If you do not get dimmer control on these lights, then you could have a broken wire in the circuit or the dimmer control unit could be faulty (the control unit is separate from the control knob assembly on the dash). You will need to download the electrical section of the service manual from the NSX Wiki and go through the test procedure set out in the manual to determine where the problem is. If the mirror and window switch lights dim correctly, then the dimmer control unit is OK and the problem may be just restricted to the instrument cluster lights. If it is just the instrument cluster lights, it could be a bad connection to the instrument cluster or on the instrument cluster circuit board. If it an instrument cluster problem, go by some Robaxacet. My back and neck hurt just thinking about cluster removal.
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Thanks for the tips. I will check the items you suggested and get back to you. Good call on checking the glove compartment light, I had not thought of that and did not realize they were on the same circuit.
Just to be clear. The dimmer unit and the glove box light are supplied off the same circuit. The power window switch lights and power door mirror switch lights along with the dash are all dimmer controlled. The glove box light is not dimmer controlled which could have been inferred from the way I wrote my response.
currently having the same issue except with my clock working and just my cluster not illuminating at all. any solutions found?

Edit:went and checked my dimmer switch for functionality and when i reinstalled it, it appears the plug that was leading into the module was not plugged in fully! it was a easy fix!
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