Commentary on the Autronic Eye
By John Oldenburg
[John Oldenberg has been restoring Autronic Eye units for over 20 years]

The first of automatic headlight dimming systems were called Autronic eyes.  They were first offered in 1952 by Oldsmobile and Cadillac.  All other divisions started 1953.  They kept this name until 1959.  1960 and up, the name was changed Guide-matic, but it served the same purpose;o automatically switch the head lamps between upper and lower beams in response to light from an approaching car.  Lincoln started purchasing Autronic eye's in 1957, Ford and Mercury and 1964.  Each had a high failure rate until they started purchasing units from Delco.  The typical system consistent of four individual units, the phototube, amplifier, power relay, and a special foot dimmer switch; or an auxiliary override footswitch.

In 1955 Oldsmobile offered the first on/off switch integrated into the headlight light switch.  This was the only division to offer this until 1962, when Cadillac and Buick had a off switch built into the phototube.  Many people asked me how to identify a Guide-matic system or an Autronic eye for their car.  I think we have all been to swap meets and seen parts or complete units that a vendor is trying to sell, but is not sure what it was off of.  If you ask the vendor, he may ask what car you have first, before he tells you it fits your car.  Or we have all heard "they are all the same in those years."  This is not true!  Some of the first clues are the shape of the phototube lens.  The square clear lens was used in 1952 through 1954 (mid year).  Chevrolet retained the square lens until mid 1955.  This was only to use up old inventory.  Chevrolet only, used 6-volt autronic eye systems on 12-volt cars with a special 12 to 6volt reducing resistor.  This was a poor idea, as it put a large load on the charging system.  But it was cheap!

The round clear lens was first used in 1954, and lasted through 1958 on Cadillac and Oldsmobile.  Buick, Chevy and Pontiac retained the round lens through 1959.  The 1959 Cadillac and Oldsmobile unit was a one-year only unit.  It represented a breakthrough in technology as this was the first of the low voltage units.  The phototube was supplied with just 2.25 volts.  This phototube was still large but the lens was oval and clear, and there was a knob on the back to adjust the sensitively while driving.  There was one exception; a 1959 dealer installed unit that was a high voltage DC unit.  The amplifier was mounted behind the kick panel (all amp's were there in 1959 through 1962 in Cadillac, all others 1958 through 1962).  This phototube had a knob on the back of the eye, as well as a clear round lens.

There was a large black box, or amplifier, under the hood of the car.  If it had one adjustment knob under it, it was used for 1954 and earlier (1955 and earlier for Chevy).  This was a high voltage DC unit.  If it had two knobs, this was a high voltage AC unit, and was used in 1955-58.  In the hight voltage AC units the phototube was supplied with up to 1000 volts to operate the system.  1958 was the last of the large amplifier under the hood for Cadillac and Oldsmobile.

In 1955-58 Oldsmobile used a rubber isolation system on the amplifier to reduce shock or harmonic vibration.  This had 2 separate metal legs and 4 large rubber isolators.

The 1960 phototube was another breakthrough.  This was the first year of the small phototube.  It had an amber color lens to make the system less sensitive to fog or snow.  The earlier ones had this as well, but it was inside the phototube housing.

In the Cadillac division only, the phototube was removed from the dash in 1964 (unless it was a dealer installed unit or a professional car), and installed behind the fender or grill.  These units are unserviceable and should be replaced if not working.

The first and only year to sport a "safety salute" was 1960.  It utsed a two-step relay.  When the headlamps were switched to low beams the upper beams would remain on at a reduced candle power for one to two seconds to indicate the car was equipped with a Guide-matic system.  This was a great idea, but a poor design, and thus had a very high failure rate.  There was several attempts to salvage this part of the system by the GM tech department, but by February of 1960 GM sent notification to all dealers to disconnect this part of the Guide-matic system if there were problems.

The phototube mounting changed almost every year with the new contours of each dash.  You have to make sure you have the correct one for your car.  On a Cadillac it is easy to make sure you are mounting the phototube in the correct location, as the holes are there for you, in the steel dash anyway.  Just take a awl and poke a hole through from the under side.  For other divisions you must have a template, mark and drill a hole from the top.

The next clue to check is the serial number printed on a paper sticker on the amplifier.  If the amplifier was mounted under the hood of the car for a long time the tag may be deteriorated and fallen off.  The phototube had a metal tag in the years 1952 through 1959, and a paper tag between the phototube and mounting in 1960 through 1966.  The serial number consists of nine digits.  The first digit indicated the GM division the unit was sent to.  The second and third digits indicated what year the unit when into.  The remaining 6 digits indicated the serial number starting with number one.  If you run across a very high number starting with the 100,000 range, this means there may have been a minor mid year production change.

Here is a breakdown of the model and serial numbers as they apply to the various car lines;

156 000001 Chevrolet
256 000001 Pontiac
356 000001 Oldsmobile
456 000001 Buick
556 000001 Cadillac
6--   ----------  (The number 6 was GMC truck division and no automatic headlight dimming system was ever used in trucks.)
756 000001 Warranty Replacement
857 000001 Lincoln (An "A" will follow the serial number 1964 and up.)
864 000001-B Mercury
864 000001-C Ford

*There is a exception to this coding.  In 1952 this system of numbers was not used yet, but it still had a serial number with all 9 digits.

The Autronic Eye in the 21st Century

Intellibeam, an option on the 2005 Cadillac STS, is a new way of controlling high-beam headlamps.  The concept is not new. In 1952, Cadillac introduced the Autronic Eye system, which used a dash-mounted sensor to automatically dim the high beam headlamps for oncoming traffic.  Intellibeam does this too, but in a much more sophisticated way.

Using a small light-sensing chip that is able to detect light similar to the way the human eye does, Intellibeam will turn off the high beam headlamps as oncoming traffic approaches.  Rather than switching directly from high-beam to low-beam operation, the Intellibeam system gradually dims the high beams as approaching vehicles get closer.  The high beam indicator on the dash shows they are either on or off, but the actual operation of the high beams provides gradual dimming or increases in illumination.

This is a great safety feature.  Normally, when headlamps are dimmed from high beam to low beam, there is a period of time when the space between the two vehicles is dark and hard to see.  Intellibeam provides maximum illumination all the time, eliminating these difficult areas.

The Intellibeam’s digital light sensor and electronics are located in a module mounted on the back side of the interior rear view mirror.  The light sensor analyzes the light colour, intensity and movement to distinguish between vehicle lights and other light sources along the roadside.  This was a problem with earlier automatic dimming systems, which could be triggered by street or yard lights, or illuminated signs, causing the high beams to flash off and on. I ntellibeam is designed to ignore non-vehicular light sources.

The Intellibeam module controls a high-beam headlamp driver module.  This module looks just like a relay, but is a solid-state device that uses pulse width modulation - a rapid on/off switching of the voltage on a circuit — to control the output to the headlamp filament.