Digital Dash stays dark 90% of the time, sometimes comes on with correct reading

COULD BE INSIDE THE CLUSTER.GM HAD THAT ISSUE IN THE EARLY YRS

I am troubleshooting the same problem with my 1988 cutlass supreme. The instrument cluster is the same one used in the 1988 to 1993 Cutlass Supreme. The digital display (fuel level/speedometer/odometer) goes blank intermittently while the indicator lights work fine. I replaced the instrument cluster and headlight/dimmer switch (from the salvage yard) but this did not correct the problem (the dimmer does not properly work on the digital display). *** Three fuses power the instrument cluster: ELECtric (always hot), CLUSTer (hot in run), and INDICator (hot in run/start/test). These checked good with a test light. The speed sensor wires through the ECM (Engine Control Module) to the Instrument Cluster. The fuel level potentiometer apparently wires directly to the Instrument Cluster. Also, the odometer retains mileage information in its memory, and should remain with the original vehicle. *** I removed the gages (fuel/speed/odometer) and desoldered and removed the power supply (this opens the circuits) and inspected the main board of the old cluster with an ohm-meter. I then inspected the main board of the old cluster with an ohm-meter. No defects found. However, the IC (Integrated Circuit) chip on the fuel level gage is charred. All other gauges, including the salvaged gauges, have no visible defects. *** Each gauge has a row of contacts that are electrically connected to the main board via spring loaded contacts (the gauges are NOT interchangeable because their mounting points are uniquely aligned to their installed positions). The contacts are solder coated and the contact points are indented, possibly from chafing over the years, which may have degraded the electrical connections. I re-melted these contacts on the old board by smearing flux and adding a small amount of silver solder to each contact. *** Still no success! *** UPDATE January 3rd 2016 *** I have not yet found the problem, but I did conduct some further testing. Checking the fuses (previously) did not test any downstream connections. The wiring diagrams show the digital display having a separate ground. I disconnected the cluster and checked for continuity from the two connector ground plugs directly to the negative battery terminal. I also checked for power between the orange hot plug to each ground. Both tests were good. *** I also replaced the ignition switch (and turn signal harness) on the possibility the old switch caused an electrical open (power or ground) to the digital display. *** Curiously, this problem was repaired by a professional mechanic in 2001 – and the problem returned a couple years ago. It does not appear that he replaced the instrument cluster (at least with a new one, even though they were available at the time). I now have two spares I picked up at the salvage yard but installing them did not fix the problem. *** UPDATE January 8th 2016 *** I set up a power on bench test for the instrument cluster. This required use of the headlight/interior dimmer combination switch. I have four of these switches I collected from a local salvage yard. The dimmer function has two pathways: a pulse function for lamps, and a potentiometer function for the digital display. After testing the system with each three of the four switches, I believe this may be the source of the problem. Fortunately, new switches are still available (eBay), although they are a bit pricey (I just ordered one for $65). It is also easy to replace. As time permits, I will attempt repairing a switch. After the new switch arrives and weather permits, I'll post my results. *** UPDATE February 3rd 2016 *** I returned the switch because it was a used part, so I 'll explain my previous testing results. *** The instrument cluster has two banks (upper and lower) of connector pins labeled 1 through 16. The lower bank is dedicated to indicator lamps while the upper bank is dedicated to the digital display (pins 3-7) and power (pins 8, 12, 13, 15, and 16). The orange (always hot) wire connects to pin 8. The pink/black (hot in run) wires connect to pins 12, 13, and 15. Pin 12 powers the digital display. When the ignition switch is turned to RUN without starting, the pink/black wires read 12 volts and green (pin 5 speed signal) wire reads 4.8 volts. Black grounding wires connect upper pin 10 and lower pin 7. *** On the upper bank, the gray (pin 3) wire is a pulse dimmer while the brown/white (pin 6) is a potentiometer dimmer input (perhaps a switching function) and the yellow (pin 6) wire is 0-12 volt potentiometer power supply that is hot when the headlight/parking light switch is ON. A brown wire (hot when headlight/parking light switch is ON) leaves the headlight switchbox, runs through a fuse, then converts to a green wire that returns to the switchbox, which is internally split into the pulse/potentiometer functions. *** During bench testing, with appropriate voltages supplied to all hot-in-RUN connector pins on the instrument cluster, the digital display remained off until I disconnected upper pin 5 (4.8 volts D-cell batteries in series). Note that pins are always connected or disconnected with 12V power supply off. Afterwards and since then, the digital display lights up (speedometer displays zero and fuel reads full). However, the dimmer function does not work properly (only one illumination value) when adjusting the slider (there is maximum illumination when headlight/parking light switch is OFF or when dimmer is set to MAX). Also, the odometer reading is intermittently scrambled and two toggle switches (SELECT and RESET) do not work (E/M however works properly). I get the same results with two spare headlight/dimmer switches. *** After installing this instrument cluster in the car (and changing out the odometer), the digital display was dark for three days of driving (and several shutdowns and restarts). Then the digital display lit up has has been working since (about three weeks). The odometer is still erratic but the speedometer and fuel gauge work properly. I don't know what I did to cause the repair because I couldn't repeat this with a spare instrument cluster (using spare headlight/dimmer switches). This appears to be an electronic reset problem where the parts may not really defective or damaged.