headlight toys for your Cadillac

The Guidematic / Twilight Sentinel switch fitted on my '76 Eldorado Convertible

A brief overview of the two systems is as follows. The Twilight Sentinel system utilizes an amplifier unit and a single photocell to gauge the amount of outside light and turn on your lights as required. Additionally, it incorporates a delay timer to provide light for you once you have exited from your car, and an additional cornering light selection of left to right by using the turnsignal switch depending on which side of the car you would like to illuminate other than the front and rear. The Guidematic system automatically senses oncoming light using a grille mounted photocell and a fairly standard electronic dimmer relay and dims your high beams when oncoming lights are seen. A special footswitch is part of this system and is the secondary on-off switch for the system.

I am most familiar with the 1974-76 (& '77-78 Eldo) dash layout so I will base it on these cars. Slight differences may be present but I will try to provide a general scope for the project and things for all years to look out for.


If you are converting from a standard setup without either of these features, you will need a fair amount of stuff. If you want to do just the Guidematic or just the Sentinel, read selectively from the information beneath. I strongly recommend taking a lot of extra dash screws et.c. as you may find that you need some along the way. Remember where things came from and how you got them. DO NOT CUT ANY WIRES - YOU DO NOT NEED TO DO THIS EXCEPT IN EXTREME CIRCUMSTANCES, AND THEN REMEMBER HOW THEY ALL GO BACK IN.

The Twilight Sentinel amplifier unit mounted to the lower steering column crossmember.


The Guidematic eye through the grille




The headlight harness connector from the main wiring harness to the switch.

Remove your lower steering column cover beneath the dash. Inspect your wiring from the multi-pin connector running to the headlight switch for broken wires, rigged fixes, et.c. In my case I had some very juvenile fixes performed to my headlight wiring and acquired a pigtail from the main harness from another car at the junkyard and spliced this in. Reach your hand around to the rear portion of the headlight switch in your car, there is a spring loaded button here which releases the headlight knob and shaft. Before depressing it, pull the headlight switch out to headlight position. Depress the button, and pull on the knob. It and a 6" long shaft should come out. If you like your knob better than the one out of the junkyard, put it somewhere safe. If you have the standard headlights-only switch, remove the chrome knob that remains by turning counter-clockwise. You will not need this again nor the part which falls out the back! Working under the dash, remove the lower two screw!
s for the headlight switch. Wiggle the back plate and switch slightly and it will disengage from the front portion of the switch. Disconnect the connector from the main wiring harness (not at the switch) and set this aside, you will not need it again unless you are not installing Sentinel with your Guidematic. Now remove the top two screws holding the front portion of the switch to the dash. Carefully withdraw the switch front.

Split your new switch as described before by releasing the knob and splitting into two halves. Might want to tidy it up a bit before installing in your car as it's been in a junkyard, take your time! Note the potentiometer(s) on the back of this portion of the switch, and their related wiring, and note how the front knobs work them. Make sure they work to their correct travels. Now install this portion of the switch as you removed the old front. Those upper screws are a pain in the ass! Now replace your illumination bulbs, #1816, while you have the back portion of the switch out. You absolutely need to use the Twilight Sentinel switch if you want to use Twilight Sentinel, they are two different switches. I am assuming anyone at this level of trouble is installing both systems. Good move! Is all of your wiring still connected to this switch going down to the main wiring harness? Good! Hook the upper portion of the back plate into the front section of the front, and make sure !
it lines up with the lower screw holes. Make sure you are not pinching either potentiometer harness and that they are correctly routed through the channel on the backplate. Insert screws. Make sure everything is lined up perfectly in the front. Reinsert headlight knob. Connect headlight harness connector to main wiring harness connector. There is an additional black wire with yellow tracer on your main wiring harness at this connector, find the corresponding wire on your Sentinel harness and plug it in. Plug in the Sentinel harness 3 pin plug at the front of the switch.

Now you're looking at the Photocell, aren't you? That's right, dash pad has gotta come out. From left to right, turn the 1st, 3rd and 4th vents to their most upright position. Now using a small flathead screwdriver, see the little tabs to the left and right of each vent? Holding the vent in the upright position, pull these tabs out CAREFULLY towards the inside of the vent, and remove the vents CAREFULLY. If they're flopping, now is a good time to stick some felt on with 3M Super Yellow Adhesive on one side where there once lived some foam. Vents out, remove two bolts and a nut from inside one of each of these vents. You also have four screws along the bottom edge, and the map light to remove. Pull dashpad out. Unhook the left climate control vent and stuff it down in the orifice down there. Now you can get at the photocell hole. But first, wouldn't you like to remove and replace your front speakers? 8-) Anyway, once you've done that, feed the photocell up through the great t!
angled mess and working half inside, half outside the car, push it up squarely into the hole so that all you see is the dark blue of the photocell lens. Refit dashpad, map light and vents.

Now take a break and admire that headlight switch with all the features. Go on, pat yourself on the back, but don't stop now, we're more than halfway there!


The Guidematic "Autronic Eye" fitted to my '76 Eldorado grille.

OK. Take the Guidematic harness and feed the really long portion through the big firewall grommet with the vacuum hoses in it. Run this up to the grille along the left inner wheel house. Remove the intake air scoop, and keep the connector away from the radiator and coolant tank. Now find your bracket assembly. Mount the top using the screws taken with it from the other car. They are metric, 10mm head. Fight with this and with a lower support bracket from a junkyard car or of your own design, but make sure you have something holding this from top and bottom. Once this is all mounted, put the eye on the bracket and hold it with the spring. The front of the eye has a V groove that sits on that little "shelf", and the rear portion of the spring sits beneath the "shelf" on the back of the eye. Make sure the adjustment screw is through the groove on the front of the bracket and holding. Look at the level on the Eye. Using a socket, turn the adjustment screw in until the level bubble is in the middle, just as if you were putting a new studwall in your house.

Guidematic eye connector in "nice cold place" between coolant tank and radiator.

Run the connector over to that nice cold place between the radiator and coolant tank tray. Plug it in and electrical tape it so no moisture gets in that connector. Refit the air scoop. Wire tie down the harness leading to the eye in at least 2 places so that it doesn't go anywhere it shouldn't.

Working in the car again, pull back the carpet around the footswitch and remove the old footswitch, put this aside. Fit your Guidematic footswitch. Now there is an intermediate connector between the footswitch harness and the fusepanel. Unplug this and fit the appropriate Guidematic harness connectors to this. If for some reason you do not have a connector here anymore (like I didn't), match the wiring colours to the fusepanel side, and then on the footswitch side, match as follows:

Peach wire - blue wire
Green wire - grey wire

Now plug the single green wire into the bottom terminal on the new footswitch. Plug the old 3-pin harness connector into the top. Now unbolt the leftmost screw from the lower steering column support and use this for your ground wire ring terminal. Refit. Take the 2 pin connector from the headlight switch front and plug this in, making sure to keep it and all other wires out of the way of your feet, pedals, e-brake, et.c. Find a home for the Guidematic relay, some years they clip onto the bottom of the fusepanel, others screw into the firewall. Do whatever it takes, but find it a safe home!

Take your Twilight Sentinel harness and plug it into the amplifier. This goes on the lower steering column support, 2 screws and clips. Make sure all your other connections are really really good.

Put the battery back on line. Pull the headlight switch on with the door open. Does the Sentinel amplifier buzz? GOOD! Now, turn the Guidematic sub-knob to about the middle position. Turn the lights on, wait a minute or so. Depress the footswitch VERY SLIGHTLY. While holding it down, do you get high beams? If so, GOOD. If not, FULLY DEPRESS the switch and release, and then try it. You should now have momentary high beams while resting your foot on the switch.

Turn the headlights off and turn the Sentinel and Guidematic knobs to an intermediate position. Close the garage door and turn your lights off in there or wait for darkness, then start the car or turn the ignition on at least. Do the lights come on automatically? Turn the car off with the Sentinel sub-knob in an intermediate position. Do they stay on for a little while? Put the turnsignal lever in the left hand position. Do you get a cornering light? Turn the ignition back on and note if your headlights are in high beam or low beam mode. If low beam, block the grille opening for the Autronic eye. Do they go to high beam? GOOD!

All of the operating instructions for both of these systems are in the Owners Manual and the Service Manual for your particular years. If you do not own a service manual for your car, now is the time. If for whatever reason one or both of these systems are not working properly, check back on this Guide to see if you did everything right, it is NOT hard, so you probably did. Then follow the diagnostic flowcharts in the Service Manual to figure out which of your parts was no good.