Now that the weather has improved, I'm working in the evenings to fix up some stuff in the Bonneville, so I'm going to post an occasional diary as I go. I plan to fix the flaky compass and DIC displays so they stop flickering and blanking-out occasionally, add a red alarm-like LED to the dash to add a bit of visual deterrent to back up the factory alarm (nothing more annoying than having some moron discover your alarm _after_ he'* broken in), and add a BulldogSecurity RS-102 remote starter, including dome-light supervision, parking-light confirmation, trunk release and keyless entry.
Maybe when it'* done, WillWren or I can massage it into one or more technical articles on how to do specific stuff, but for right now I don't have a plan of action beyond trying to do several things at once, so things may get a little intermixed here, but let'* get started.
First thing to do is open up the dash for a look-see. Decide to start by pulling the gauge cluster, since I'll need to be up that way anyway in order to install the LED (not sure exactly where but the area below the tach looks available), and I'll need to add a wire tapping into the parking-light circuit coming out of the headlight switch which the remote starter will be using to flash the lights.
Lower IP trim panel needs to come off first. This is the plastic panel surrounding the dash vents, 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. 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 next to subwoofer control is 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.
For lower steering column panel cover, remove four bolts, one at each corner, plus screw in support bracket holding up plastic lower soundproofing panel. Found cellphone installers in 1996 had strapped cable ties around support bracket while running cable. Sigh... (Will soon find that cable will cause more headaches further on.) Also remove lower soundproofing panel to open up area above pedals. Plastic pushpins must be backed out in order to free up ALDL connector from soundproofing panel, and yellow airbag wire must be carefully unplugged.
Using T-15 Torx screwdriver, remove screws around perimeter of upper trim panel, holding headlight switch, cigar lighter and grille for HVAC aspirator tube. Panel comes off without a major fight; reach around back and unplug cigar lighter wiring. HVAC aspirator tube has temperature sensor in front, covered with major dust bunnies, so a quick snort with the shop vac cleans it all out, and maybe temperature sensor will respond a little quicker now.
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 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.)
Six 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. 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.
Now work the gauge cluster further out of the dash, tip it further up, and reach the main harness connector behind the tachometer. 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.
After both connectors are unplugged, it'* free to come out. Carry it carefully; various mounting pins and ears sticking out are both vital and breakable.
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 or cad-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.
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; they'll scratch the plastic. Dry thoroughly with a soft towel; it should be crystal clear when you're done.
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.
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, 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.
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.
Wipe indicator bulbs clean and check all for continuity with a test meter before replacing. Replace any doubtful-looking ones. 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.
Next chapter: Installing the red LED right into the gauge cluster, hooking it up and sticking it all back together, plus a weird surprise found buried inside the dashboard...