1989 with Twilight Sentinel - how does it work?

[Posti]

My 1989 Reatta has the Twilight Sentinel switch on the left dash switch pod, but no mention in the owner's manual.  It has an indicator light that comes on and has a slider switch to set the delay from low to high.  An old post indicated that this was not available on the 1989 Reatta, but it shows up on the options list for the 1989 Riviera.  I suspect that the switch is a replacement from a later car or Riviera that does not actually do anything, but if it is hooked up, how would it work?  Does it turn the headlights off and lower them after the preset period?

[Ronnie]

...  I suspect that the switch is a replacement from a later car or Riviera that does not actually do anything, but if it is hooked up, how would it work?  Does it turn the headlights off and lower them after the preset period?

 

I think your switch was replaced with one from a Riviera too. I'm not sure how it was supposed to work. It should be covered in the factory service manual which also covers the Riv.

[MOUSE]

Slider switch all the way to left, turns off the system, slider pushed towards right turns system on, sliding switch to right varies amount of time lights will remain on after engine is turned off. if slider switch is left in "on" position, lights will automatically come on when engine is started, if there is a low light condition, such as a dark garage, or outside during night hours. there is a sensor on top of the dash that senses light level, if there is low light available it will switch lights on automatically. When engine is turned off, lights will stay on for a period of time determined by position of slider switch, further to the "left" shorter time, further to the "Right" longer period of time.

[kdirk]

Yes, it is a Riviera switch fitted to your car. Internally, the Reatta switch is identical to the Riviera part save for deletion of the slider shaft, slider face and substitution of the front housing with on that lacks the opening for the button. I have turned Rick switches into Reatta switches by removing the slider and putting a Reatta housing on them. The LED and carbon traces for the slider are present in the circuit board regardless. Even the pins needed on the connector are populated. If you go into diagnostic BCM inputs, you can watch the twilight slider value change as you move it, even though the system isn't functional in a Reatta

 

Twilight Sentinel will not function on a Reatta (except for 1991 models which did have it standard) even with the switch fitted and the option parameters programmed to enable it as there is additional wiring and a relay involved in it's implementation. Now, one could certain add it if desired, by installing the relay and needed wiring along with the switch and programming the correct option codes, but I've not heard of anyone doing so. The Reatta lighting system is derivative of the Riviera's, and so has most needed components already in place save for that mentioned above.

 

I actually kind of like it on my 91's, though the biggest issue is a failing twilight photocell in the dash. If this is out of calibration (common on these cars at this age) the system doesn't work right. The photocell can be replaced, but is rather costly (about $50-60 online) and while I've experimented with generic photocells that seem to work, almost all end up throwing a BCM 119 code for being out of range due to their resistance differing from the stock part. I've found no retail source for the actual photocell GM used (less the blue tinted carrier it is installed in) despite a major effort at sourcing it. Would probaly be a 25¢ part on its own if I could find it.

 

Kevin

[harry yarnell]

For photocells, harvest them from the Man's Mall from Buicks and Cadillacs of the period.

Chance of getting a good one is 75%.

[kdirk]

Harry, your mileage may vary as they say, but the all four Reatta parts cars I've purchased have had failed photocells, and all appear to have been factory original. Fact is, these just wear out. Cadmium sulfide, the chemical compound typically used in making photocells, appears to fail over a long time frame in such a way that it loses it's light sensitivity and then fails to operate in the resistance range required to feed the light level to the BCM. I would expect about the same on any car of this vintage (25-30 years old). Essentially, prolonged ljght exposure eventually kills the sensitivity of the device. Unless a parts car spent most of its life out of direct sunlight, I'd figure the chances of finding a good one that old are far less than 75%

 

Also important to note that around 94/95 most GM models equipped with a twilight photocell received a new design part that is not directly compatible with the Reatta, as they have a different housing and connector type, so 93 is about the cutoff in model year terms to find a compatible part. I've not examined adapting these to the Reatta, as I don't know if the photocell itself is the same or not. They are less expensive typically, but the photocell cannot be removed from the newer style plastic housing non-destructively near as I can tell from pictures online. I really don't want to buy one and ruin it to test the theory and find out it won't work after all.

 

One other consideration is that removing the dash pad to service it is a risky proposition, as breakage of the plastic or cracking the forward soft part of the dash top in the process is very (ok, way too) easy. So, if replacing it, I'd want to put a brand new one in to be certain I'm not going back in again in a few months time to replace a failed used one. These are a massive pain to get access to the way the dash pad is designed, so the fewer times it in needs to be done, the better.

 

I'd point out that even in cars without Twilight Sentinel, the photocell needs to be working so as to ensure the display dimming and switchgear backlighting work properly in the dark. The usual failure mode is for the photocell to read light at all times, thereby fooling the BCM into thinking it is never dark. This then prevents the VFDs and CRT (or climate panel/radio on 90/91 cars) from dimming at night and the legends on the headlamp, washer (88/89) console switches and the shift indicator from working properly.

 

The other poor man's fix would be to hardwire a resistor at the dark end of the resistance range to simulate dark conditions at all times. Then, when the fog/park/headlamps are turned on, the dimming and switch backlighting will work regardless. The trade-off is that if you run lights all the time for DRL's, the displays will dim during the day when you want them at full brightness. Also, in 91 models you'd have to leave the twilight sentinel off at all times as the headlamps would popup on full daylight otherwise. This is much like the VATS key pellet bypass trick to allow the use of standard ignition key blanks and eliminate the chance of being stranded by a bad key pellet or broken ignition cylinder pellet sensor/column wiring. Also in the same vein as the the air bag resistor bypass trick to eliminate the SIR telltale when substituting a non-SIR steering wheel in 90/91 models.

 

Kevin

[Ronnie]

If the sensor hasn't completely failed and is just reading out of range it can be "helped" by adding a resistor in the circuit.

 

When I got my car the instrument panel lights wouldn't dim at night.  I added a resistor (sorry I don't remember the value now) and it has worked since,  although sometimes I have to push the dimmer slide over get the panel lights to brighten up in the daytime in low light conditions. It's not a perfect solution but it is a good compromise between taking a chance on breaking the dash or having the panel lights glowing full bright in your face at night.

 

I have another good sensor.   I just dread taking a chance on breaking the dash to change it out.

[harry yarnell]

Sorry Kevin, I'm sticking with my 75% estimate. I harvest these when I'm up at the yard; I must have two dozen of these. I measure the resistance covered ( dark) and uncovered (light) and check the differential resistance. Off the top of my head, I can't remember what resistance values they are, But I get about 25% failure.

As for access, most are mounted to a 3' X 1" defroster grill that just pops out; no dash removal.

It's in my hand in two minutes.

Yes, some of these are mounted in a little blue holder held in place with a 7mm screw with a pigtail. Add another 5 minutes.

I havn't done it, but it looks like it can be disassembled and cobbled into the plug-in version.

[kdirk]

Harry,

 

that surprises me but I'll defer to your experience. Based on my own sampling here, my two 88's and both 91's, all four needed new photocells within the last four years. The 88 due to be parted here come spring is also bad. All three I've parted here already have also had bad photocells (or at least close to fully failing) based on testing the resistance just as you described. I call that a 100% failure rate, but maybe these things just hate me personally (chuckle). I know a sample size of 8 isn't enough to make a statistically acceptable statement, but based on that I really thought they were more likely than not to be bad now. If you are finding good ones, that's great. Let me know what you are selling them for, I may be interested in a couple of spares.

 

As far as access, yes once the defrost grille and dash pad are out, access is easy. Getting the grille and pad off is the bad part, as they are so easy to damage. If you are harvesting from parts cars, I suppose one can be less mindful of removing the trim pieces intact, but in my own cars I need to keep them undamaged.

 

The later version used from circa 95 onward is in a bubble shaped blue plastic holder. My Cadillac has this version, the Reatta uses one that resembles a flat topped 194 bulb (has a wedge base) and is open frame. The wire leads of the photocell can be unwrapped from the holder and removed from it. I've done this to install a new photocell in it (different type from OEM) and used this with varying (generally not great) results.

[DAVES89]

I've been lucky and gotten 2-3 from other cars [Pontiac Transports comes to mind] so I think I am good. I know they work as I was having a switch problem and misunderstood what Mc_Reatta was trying to tell me so tried all I had. Another item to add to my next Gibson's run. I guess if I am staying in the Reatta car business I may need more...

 Just checked and only have one in inventory. I know I sent one to Ronnie, and maybe Kevin or 2seater got one so have to "go shopping"...

[Ronnie]

I guess if I am staying in the Reatta car business I may need more...

I hope that doesn't mean you might be considering getting out.

[kdirk]

Heh. The Reatta is the Hotel California of cars. You can check out any time you like, but you can never leave. Well, at least when you get into them as deep as I have. Since there is nothing else in cars (that I can realistically afford) that interests me, I'm in for the long haul. Dave seems to be pretty well rolled up in it as well. Of course there are a few who make Dave and I look like mere amateurs, with fleets of a dozen cars and a parts stock that exceeds anything a large dealer ever stocked. I probably qualify on that latter point already.

 

Many people know me for my cars now; the Reatta has become an essential and inescapable part of my image apparently. I could have less desirable items associated with me, so I can live with that. The downside is that I can't go anywhere discretely since the car gives away my presence. Which means I couldn't hang out at the Hotel California, even if I paid in cash and put an alias on the registration. See what I just did there?

 

Kevin

[Ronnie]

I'm only allowed to have one toy at a time in the garage. I wish I had room for a parts car. Where I live they won't allow me to keep a non-running car outside. That's the reason I start to worry when I hear any indication that Dave or other parts hoarders might be thinking of quitting. I have to depend on you guys for parts. There just aren't any around here being parted out at the salvage yards.

[DAVES89]

No I am not going anywhere, as a matter of fact with the ongoing engine swap I am doing I am getting deeper and plan on hanging around for a long time. We just seem to go from one obsolete issue to another. Don't mind it, I just am glad I can drive 5 miles and look for parts off 3 Reattas, about 10 Rivs, 3 Troferos and numerous other cars I can grab parts from.

Just wish I could be farther ahead of the curve...

[Ronnie]

No I am not going anywhere, as a matter of fact with the ongoing engine swap I am doing I am getting deeper and plan on hanging around for a long time. We just seem to go from one obsolete issue to another. Don't mind it, I just am glad I can drive 5 miles and look for parts off 3 Reattas, about 10 Rivs, 3 Troferos and numerous other cars I can grab parts from.

Just wish I could be farther ahead of the curve...

 

That's good. You are a lucky man to have so many parts cars near you.