Aside from the click noise, which I can't picture as part of this problem, I'm thinking that perhaps the headlight switch rheostat for the dash lighting is flaky. If it cuts out momentarily, the backlighting circuit goes dead for an instant, and the fluorescent displays go to their full (daytime) brightness at that moment.

Next time you notice this problem occurring, try rotating the **** of your headlight switch to vary your backlighting levels, and see if that affects the flickering symptoms of your fluorescent displays. If so, you might want to replace the headlight switch; instructions for that can be found in TechInfo, via this link:

http://www.bonnevilleclub.com/techinfo/?article=39

Yep. Turns out you guys are right. The guy I talked to mistakenly thought the interior lights and the dash lights were on the same circuit (that'* where the list came from - but I was on the wrong circuit). I got a copy of the wiring diagram for the dash lights and there is no other relay in there. The headlight switch and the twilight sentinel relay are in parallel, but that’* the only relay in this circuit. I suspect this relay may be hosed, but I’m going to do a little more investigating when I have time. I’ll let you know what I find.

SM

I'm pretty sure the click is part of the problem. Or at least a symptom. The green displays momentarily go bright then back to their normal dim. This happens so fast, and so randomly, I don't time to catch everything that'* going on. I suspect the headlights lose power but it'* so quick the filaments don't have time to dim much before they are energized again, making it appear they are not affected. I'm pretty sure the backlighting in the dash changes along with the green displays, it'* just that the green displays are much easier to see. This all happens in conjunction with the same click I hear as when the twilight sentinal turns the lights on at dusk. It'* almost like the photocell detects sunlight then dark in milliseconds - except photocells don't react that quickly. Keep in mind that I'm driving while this happens, and in the interest of keeping insurance rates down, I try to keep at least one eye on the road (this thing KNOWS when I'm watching the road, that'* when it goes off!). I haven't had the time to sit in the driveway in the dark with the car running waiting for this to happen - my neighbors already watch me through their blinds wondering what I'm about, this ought to really raise an eyebrow!

The photocell should cause a delayed reaction, so I don't believe it'* bad. I'll have to look at the wiring diagrams to see where that relay is for the twilight sentinel, and also what controls it. I can't remember if it'* the RAC module.

No, the Twilight Sentinel is a self-contained module (including relay) mounted on the multi-function bracket behind the gauge cluster, IIRC. The RAC module is over somewhere on the right side, and I don't believe has any connection to this.

You're right about the delayed reaction from the photocell; I believe it'* some oddball time like 16 seconds, to prevent endless cycling on and off when driving under streetlights, for example. I know whenever I drove into a certain commuter parking garage, going at about the same speed every morning, there was one spot about halfway up the third ramp inside where the time delay would finally turn on the car lights.

Yes, it'* called the Lamp Control Module. Looks like it turns on and off the headlamps based upon the input of the photocell.

Well, I sat in the car last night for 20 minutes and the silly thing only flashed at me once, shortly after starting the car and while I wasn’t looking at the headlights (as they reflected off the garage door). Curses! So I still don’t know what the headlights are doing, but it appears the backlights on the dash dim, and the green lights on the DIC, radio, etc. go bright when the relay (lamp control module) clicks.

I played with the headlight switch a little afterwards and the rheostat and switch work fine, no amount of jiggling, tweaking, or cussing seemed to affect it’* operation.

I also played with the twilight sentinel switch, turning it off & on. By turning this off & on quickly I can almost duplicate the clicking sound. There’* no way to manually switch it off then on fast enough to exactly duplicate the sound – it happens in a fraction of a second.

Could be that the car has to be moving for my problem to exhibit itself, but I don’t think so. I’d still like to know if the headlights are being instantaneously switched or not, so I may have to grab a bag of Doritos, fill the tank with gas, and see if I can catch this thing. I imagine my neighbor will be watching out the window with a phone in his hand, 91 already dialed, and finger perched over the 1. I reckon I'd do the same if I saw someone sitting in his car watching his garage door as if it were a drive-in movie.

Yes, that'* the suspect relay that you're working manually when you turn off the Twilight Sentinel switch.

Yeah, okay, well, I'm going to suggest that that is the problem right there: the relay is dropping out intermittently. Before splurging on a new Lamp Control unit (I suspect the relay is an integral part of it), I would suggest just removing and reinstalling it, to ensure that its connections get a little scrape-cleaning in the process of unplugging it all and plugging it in again. This might be all that'* needed: to deliver full juice to it.

I have some vague recollection of reading in Telecom Digest many years ago (comp.dcom.telecom newsgroup) that some phone switching systems will complete the last "1" and route the call to Emergency Services if the user presses 9-1 and then leaves the line open without further dialing for some period of time. Probably not a good idea to test that theory, however...

Got some new information on this little nuisance. It'* really, really intermittant, but Kim & I watched what'* going on and we agree that the radio & DIC lights brighten, the dash backlighting does NOTHING, and the headlights stay ON. Quite interesting.

And I have another data point. Yesterday as I drove under a bridge in the afternoon the lights switched on (waaay too fast) and the turn signal slowed down. The voltmeter dropped well below 14V. I'm thinking it'* time for an alternator. This may be part (or all) of my problem. At least its something I need to correct before going any farther.

Good advice, if the LCM is suspect, to re-mate the wires going to it. Might just be a little corrosion in there!

More to come...

I'll let you know if the cops bust down my neighbor'* door before he finishes dialing!

Well, the fluorescent displays are losing their connection to the dash backlighting circuit: they're supposed to detect that the dash backlighting is on, and adjust their own displays to match it. (In fact, if you turn the headlamp **** rapidly to brighten or dim your gauges quickly, you can see a small but definite lag before the fluorescent displays catch up to the new setting.)

Agreed. It'* not too hard to pop the alternator out for bench testing (most auto-parts places will do that for free) to get an output test done. I'm on AC-Delco alternator #4 myself; Nos. 2 and 3 both quietly died in service. They just stopped putting out juice, and eventually the car couldn't run on the battery anymore. (It'* surprising how long it _can_ run on the battery, but that'* another story. )

The behavior of the Twilight Sentinel in my car changed noticeably after the battery got a full recharge not too long ago: it started working almost perfectly for the first time in a long while. (Most of the time mine is hypersensitive to light and won't keep the car lights on in anything less than total darkness.)

There'* a bit of a history of that, yes.

Right; always best to test these theories on a neighbor rather than yourself. That'* what they're there for.

Update:

As you can see, this problem is not annoying me enough (yet) for the evil eye of Mordor to focus all its attention on it! I did change the alternator and I'm charging at 14+ volts again, but this didn't solve the problem.

The problem seems to be exacerbated at dusk. I notice a lot more switching of the green lights as the sun is just going down compared to when its dark out. Obviously there is no switching in midday conditions as the twilight sentinal is not active.

Also, I noticed that it will turn the headlights on as I pass slowly under a bridge. This is expected after a several second delay, but it happens rather quickly these days.

Another data point to consider.

More to come, eventually...