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.
PARTS YOU WILL NEED
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
The Twilight Sentinel amplifier unit mounted to the lower
steering column crossmember.
The Guidematic eye through the grille
- Headlight switch, you need the whole assembly as there is a potentiometer
in the front portion of the switch which controls the Sentinel Delay. 4
screws to the support member holding it and the climate control/cruise
switch to the dash.
- Sentinel amplifier - large white box found on the lower steering column
support crossmember or suspended in the area of the steering column otherwise
by two screws and clips. Inspect the amplifier you want to use for the
plastic case separating from its other half, breakage of this plastic,
missing label over the adjustment screw, et.c.
- Headlight switch/Sentinel harness - everything unplugs so don't cut
anything, the main harness connector to the main wiring harness connector,
one pin black/yellow wire at the main harness but separate, three pin at
the switch, and wide single row multi-pin at the amplifier itself. The
black/white wire attached to this harness is the photocell, which is mounted
in the left front speaker grille. I got lucky once and was able to just
pull it straight down and out of its sprung clips up there but recommend
you remove dash pad and take it out the normal way so not to bugger the
harness or the photocell.
- A few good spare climate control vents.
NOW, THE FUN BEGINS!
STEP ONE: DISCONNECT YOUR NEGATIVE BATTERY TERMINAL!!!
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!
- - Autronic eye - the eye, bracket, plastic front extension are pretty
common but the diagonal support member going to the centre grille support
is not. Make sure you have the right one or make one to fit when you get
home, but take all of these parts. Recommend you remove the eye from the
bracket by releasing the spring and then remove the bracket and rod assembly.
Also make sure that the bracket holding the unit to the top of the grille
has your body type hole marked at the top (i.e. C or E) or it might not
line up with the tapped holes in your grille.
- Guidematic headlight switch - most of these have Sentinel too, so if
you're doing both systems, deep-six the Sentinel headlight switch you got
from that other car and use this one in your car. The cars with two systems
have two rheostatic potentiometers in the front portion of the headlight
switch assembly as one unit.
- Guidematic footswitch - these have the normal three pin connector on
the top side like a standard switch and then a single pin connector on
the bottom unique to the Guidematic setup. This is a 2 stage switch so
you can momentarily have your high beams on by slightly depressing this
footswitch when Guidematic stipulates you should be in low-beam. (Like
to tell that &^&^%$*%^ to turn his high beams off that's coming
at you in the other lane!)
- Guidematic wiring harness, relay, and relay terminal: two-pin connector
coming off the front of the headlight switch, one pin at footswitch proper,
two three-pin connectors in and out of the footswitch wiring going to the
footswitch and from the main fuse panel, 3 pin going into engine compartment,
1 ring terminal ground wire. Gingerly remove the 3 pin from engine compartment,
it should be going through the grommet which brings vacuum to the climate
control and cruise vac dump switch.
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
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
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
FOOTSWITCH SIDE Blue wire - purple wire GUIDEMATIC HARNESS SIDE
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
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.