(Coming soon to the TechInfo listings as well...)
These instructions cover the steps required to remove the gauge cluster from a 1993 Bonneville SSEi. They will probably cover the same process from model years 1992-1999, with some detail variations (e.g. models without the full gauge package and/or tachometer may have only one harness connector in back instead of two; lucky you). You may need to improvise or figure out other details as you go. In case of major mistakes, notify me (acg_ssei) in the Bonneville.com forum.
Let'* get the disclaimers out of the way first:
FOLLOW THESE INSTRUCTIONS AT YOUR OWN RISK. THEY ARE PROVIDED FOR YOUR INFORMATION ONLY, SUMMARIZED FROM FACTORY SERVICE MANUALS AND PERSONAL EXPERIENCE, BUT ARE NOT GUARANTEED IN ANY WAY. IF IN DOUBT ABOUT ANY STEP OF THE PROCESS (OR EVEN BEFORE YOU BEGIN), CHECK WITH A PROFESSIONAL MECHANIC.
The most common problems reported in Bonneville gauge clusters are flickering or non-functioning gauges and/or displays (e.g. Driver Information Center, Compass). These failures may be caused by nothing more than oxidized connector pins in the many connections between components and circuit boards that make up the gauge cluster. Simply unplugging the components and putting them back together again can be sufficient to restore full operation, since the process scrapes clean the contact pins and sockets as you go.
1) Lower Instrument Panel (IP) trim panel needs to come off first. This is the plastic panel surrounding the dash vents, Heater/Ventilation/Air-Conditioning (HVAC) and stereo, plus subwoofer if so equipped. Removing it will reveal the lower screws for the upper surround panel (the part containing the headlight switch and cigar lighter), and the upper screws for the lower steering column panel cover. Jam fingers into various edges of trim panel and pull firmly outwards until clips let go. You need to move cautiously here: just use fingers, not a screwdriver, and pull until a clip lets go, then move a few inches along and pull the next clip, etc. Work around the whole perimeter of the panel, and once all the clips are popped, it'll be loose. Clip at lower left of subwoofer control (if so equipped) may be especially nasty. Once panel is loose, reach behind to unplug subwoofer control wiring, and remove. Stow panel in trunk since we won't be reattaching it anytime soon.
2) For lower steering column panel cover, remove four bolts, one at each corner, plus screw in support bracket holding up plastic lower soundproofing panel.
3) Also remove lower soundproofing panel to open up area above pedals. Unscrew stamped wing nuts at lower front corners and screws along upper edge where necessary. Plastic pushpins must be backed out in order to free up Assembly Line Diagnostic Link (ALDL) connector from soundproofing panel.
4) Unplug yellow airbag wire carefully. Remove small green locking clip (small flat-blade screwdriver may help to back it out), then press large main release tab and pull connector apart.
5) Remove the headlight switch **** by pulling it out to the On position, and feeling around the back of the **** for the ear of a spring-steel metal clip that holds the **** on to the shaft. Press the ear of the clip inwards to the back of the **** (i.e. towards you) to release its grip on the shaft (a small flat-blade screwdriver may help here) and pull the **** off the shaft. Pull the Twilight Sentinel control ring off, if so equipped. Don't forget to turn off the headlights.
6) Using T-15 Torx screwdriver (or, in a pinch, an Allen hex key of the right size), remove screws around perimeter of upper trim panel holding headlight switch, cigar lighter and grille for HVAC aspirator tube (for cars with electronic temperature control). Panel comes off without a major fight; reach around back and unplug cigar lighter wiring. Remember that orange lighter wire is hot at all times, like now. HVAC aspirator tube has temperature sensor in front, probably covered with major dust bunnies, so a quick snort with the shop vac should clean it all out, and maybe temperature sensor will respond a little quicker now. Stow the upper trim panel in the trunk so no one sits on it by mistake.
7) The gauge cluster can now come out in one piece after some major fiddling. We can leave the clear lens in place to protect the gauges in the process. The steering column is dropped down an inch or so for clearance by backing off the two large nuts (approx. 15mm size) on the column support. (Don't take them completely off: the column will not fall down by itself right away, but in a moment of absentmindedness you will lean on it and get a big surprise. Yup, I did.)
8 ) Six T-15 Torx screws come out around the edge of the cluster housing, and it can be wiggled out an inch or two, and tipped upwards slightly. Be _very_ careful to avoid breaking off the large white plastic ears of the mountings you just unscrewed. For cars with the full gauge cluster, reach around the right end to get at the right-hand wiring harness plug: press in its retaining clip, then work it off its multi-pin connector. It pulls straight out the back of the cluster, but requires some wiggling before it will let go.
9) Now work the gauge cluster a little further out of the dash, tip it further up, and reach the main harness connector behind the tachometer (or speedometer, for base-model cars). Again, press in its retaining clip, then work the plug straight off the back. This has even more pins than the last connector, and also does not want to come loose right away.
10) After both connectors are unplugged, the cluster is free to come out. (These cars do not have mechanical speedometer cables.) Drop the steering column further down if you need more clearance to get the cluster out. Carry it carefully; various mounting pins and ears sticking out are both vital and breakable.
11) Spread a soft towel on the workbench and lay it down either way up, depending on what you need to work on. There are two basic lengths of T-15 Torx screws holding everything together: shorter gold-colored, cadmium-plated screws, and longer gray steel ones. Do _not_ mix them up: bottoming out a longer screw in a short mounting sleeve can snap the plastic real quick. PAY ATTENTION TO WHICH SCREWS GO WHERE. You are removing the first of many screws you will encounter, so making notes on a piece of paper will help you later.
12) To clean the front lens, remove the perimeter screws and lift off. Wash it in a sink with a flood of warm water, some hand dishwashing detergent and maybe a soft wet cloth, although I just used my fingers to wipe on a layer of detergent, then rinse it off. Do not use paper towels for either washing or drying; they'll scratch the plastic and leave it foggy or hazy. Dry thoroughly with a soft towel; it should be crystal clear when you're done.
13) The gauge cluster is one of the more complicated ones I've seen, driven by a set of circuit boards twice as high as the cluster itself, folded over into two layers in order to get everything to fit. To service the bulbs or otherwise dismantle the back, remove the backing plate by removing the perimeter screws and those next to the harness sockets (but only those holding the backing plate). This should reveal a large circuit board across 2/3 of the cluster, and a separate one on the end. Several plug-in ribbon cables connect the boards to each other _and_ to the second layer of circuit boards underneath.
14) Carefully lift up the main board and the end board. Each board is plugged on to one or two gauges by contact pins sticking out the back of each gauge (4 per gauge) that fit into clips on the circuit boards. Removing the boards involving unsnapping some small spacer pins near the edges which are snapped into small holes in the boards, then pulling the boards gently straight up off the gauge pins, then unfolding the boards by their ribbon-cable connections to reveal the other circuit boards underneath.
15) Unplug the ribbon cables to release the circuit boards. Two ribbons connect the main board to the end board; a couple more connect major components like the compass and DIC displays. Ribbons unplug at only one end, and some disconnect sideways while others pull straight up. Figure out which is which before yanking on any of them. A tiny screwdriver may help to work loose the connectors, but make sure you know how each comes apart before you start prying on it.
16) Wipe indicator bulbs clean and check all for continuity with a test meter before replacing. Replace any doubtful-looking ones. Bend the ears of the bulb sockets up a little bit for a good contact, and use a pencil eraser to buff the contacts shiny. In the case of the large wedge-base bulbs like #194 or #168, replace them only with the same number replacement; some burn hotter than others and the wrong bulb can cook a socket. If you can't read the number on the bulb, match it by the color of the little ceramic blob inside it on the filament support.
17) Look for cracks in soldered connections, especially where ribbon cables plug in. I was lucky and found none; my flickering displays were just due to oxidized connections, and the process of unplugging and reassembling was all that was needed to restore a solid display to the dash. If you find an obvious crack, use a hot pencil-tip soldering iron to melt and reflow the solder where necessary. Be careful here; a replacement cluster can run a few hundred dollars, so if you're not comfortable with pinpoint soldering, paying a pro for the repair at this point will be a lot cheaper (since you've gone to the trouble of pulling the board yourself).
Reassembly is the reverse of the above. You knew that.
Most importantly, be sure to put the screws back in the correct holes; if a screw seems to be bottoming out, back off and doublecheck that it'* the right one for that location. Don't overtighten anything; hand-snug will do fine, except for the two large steering column support bolts which should be good and solid.
When you're done, you should be rewarded with a clean, clear, sharp display, and really crisp red backlighting at night. You'll marvel at how fuzzy it had gotten over the years, and how you hadn't even noticed it until now. You'll want to buy another Bonneville just so you can do this all over again.