Twilight Sentinel question

[Mike]

Hi everyone!  When Im using the twilight sentinel on my 71 Eldo, there is no time delay--the lights turn off and on instantly, such as when passing under a viaduct--the lights will turn on in an instant, then turn off the second the light hits it again.  If I am driving through a parking garage, the lights will flash off and on just from passing under a fluorescent ceiling light!  I read in the shop manual about a "time delay circuit," but this problem is not addressed.  I suspect there is no way to adjust this. Im not referring to the time delay of the lights staying on after the ignition is shut off--that works fine.  Has anyone ever successfully adjusted the time delay, or do I need to replace the whole amplifier and PE cell?

Mike #20545

[Barry M. Wheeler #2189]

Have you checked the "bulb" in front? Is it completely covered with dirt, etc? That might be why it is so sensitive? There might be just enough gunk on it to make the difference. Im not a "guru" on these things, this just happened to jump into my head. Anyhow, its easy enough to check tomorrow. Good luck.

[Dick Heller]

I keep my photocell covered with a small piece of electrical tape so the lights are on continuously.

[Davidinhartford]

You have a bad twilight sentinel box.    Look under the driver side dash and you will see a milky white/clearish box with a rectangular plug going into it.     There is a sticker on it that reads:   "Replace as pair with photocell".   But you can swap out the module without changing the photocell.  I have without problem.

The twilight sentinel is a simple system.  It has three parts.

1)   The photocell up under the left speaker grille.   Detects ambient light.
2)   The control ring around the headlamp switch.  Turns it on/off, sets the shut off delay.
3)   The control module which is the brain.     There is a relay in there that prevents it from reacting to shadows or streetlights

[Glen]

The time delay circuit can be defeated with a screw on some models for adjustments on the bench.  If someone has screwed that all the way in there will be no time delay turning the headlights on or off. 

If that is not the case then you probably have a bad capacitor in the circuit.   

IIRC the way this thing works is the photocell (or is it a photo resistor?) controls an input voltage to a Schmitt trigger.  The Schmitt trigger has an output either on or off so the light level does not affect the time delay. 

The time delay is a resistor and capacitor that charges/discharges at a fixed rate. 

The time delay circuit operates a pilot relay that operates a power relay for the lights. 

The delay bypass I mentioned above just shorts out he capacitor so there is no time delay making it easier to set the threshold of the Schmitt Trigger. 

HTH
Glen