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: 84 Headlight Motor


dirty dan
12-05-2007, 06:17 AM
I just ordered a gear set for my headlight motor. Is there anything I need to know about before I go back in and re-install? How does the motor know when to stop? I didn't notice any limit switches on this unit.

onedef92
12-05-2007, 09:20 AM
There are two motors, and three relays in the system. Here's how it works:

The headlight door motors reverse direction by reversing polarity. However, the automatic shut off (high torque switch, or HTS) makes that a rather more complex task than at first it might seem.

That's because when a motor reaches its limit, one of the 'wires' is disconnected from the motor by the HTS. Reversing the polarity at this point wouldn't do anything since the circuit is broken by the HTS.

Consequently, each motor has three wires for control. The combination of the blue wire, gray wire, and green wire provide polarity reversal to the motor (to make it able to run in both directions) and to run each motor from its resting state, after it has shut off.

There are of course two motors. They operate and are controlled identically.

Here's the matrix:

RIGHT HAND MOTOR

Blu Grn Gry
up: (+) (-)
dn: (+) (-)

That is, in order to run the motor up, the system connects the green wire to the hot side and the gray wire to ground. In order to run the motor down, the system connects the blue wire to the hot side, and the green wire to ground.

The left hand motor operates the same, except for its blue wire is actually blue with white stripes.

There is an actuator relay for each light mounted on the body of the light housing. There is also an isolator relay, mounted on the fender wall on the driver's side. When operating properly, the two actuator relays act identically.

The actuator relays get their instructions from the isolation relay. When the motors need to run down, the isolation relay is not energized, the blue (and blue/white) wires make with the hot side through the closed contacts of the isolation relay (which is not energized), and the ground is furnished to the motor through the closed contacts of the actuator relay until the circuit is broken by the HTS. When operating properly, neither the motors nor the relays draw any current in the full down position.

When it's time to go up, the actuator relays are energized when the pink wires coming from the isolation relay are connected to the hot side through the newly closed contacts of the isolation relay, the isolation relay is energized because the yellow wire coming from the head light switch is now hot.

When the actuator relays are energized, they furnish 12v from the always hot red wires, through their newly closed contacts, to the green wire. The motor is grounded through the newly closed contacts of the actuator relays. The motors will run up until the circuit is broken by the HTS. When operating properly, with the light doors in the full up position, all relays are energized and draw current, but the motors do not.

There are very counterintuitive things about this circuitry: When the motors are running UP, both the hot side and the ground are furnished by and through the actuator relay. However, when the motors are running DOWN, only the ground is furnished by the actuator relay because the blue and blue/white wires do not run to or through the actuator relay.

Similarly counterintuitive, when the motors are running down, the hot side is supplied by and through the isolation relay, but when they are running up, the hot side is supplied not by and through the isolation relay, but through the always hot fusible link.

That's how the headlamp door relays and motors work. The relays are not cheap but not terribly expensive, either: $17 ea for the actuator relays and $25 for the isolation relay. Proper trouble shooting can save a buck or two.

It is fairly easy to swap the actuator relays from side to side. If the symptoms change with them, then its probably the relays.

Although the actuator relays look similar to the isolation relay, they are very different, they cannot be swapped. Please not that the system is very interdependent, and it's easy to see why Chevrolet changed to electronic (as opposed to electro-mechanical) controls.

dirty dan
12-05-2007, 02:38 PM
Thank you for your reply. That is excellent information.

dirty dan
12-14-2007, 05:26 PM
Thanks again onedef92!!!!
My right relay was bad and your in-depth information was a lifesaver.

onedef92
12-17-2007, 10:27 AM
Thanks again onedef92!!!!
My right relay was bad and your in-depth information was a lifesaver.

Another satisfied customer.... ;) :thumbsup:

Sagea84
12-18-2007, 05:56 PM
I'm trying to avoid costly issues of taking the Vette to the Vette shop here so...

I replaced the gear with a bronze one and before, it had kept grinding when you turned the motor up.
Now, when you turn the motors down, it sounds like the motor is trying to keep turning after it has already shut all the way.

Could this be a bad relay? I don't really understand electrical stuff without diagrams, so I can't pick through that info myself, haha.
It can't be the gears, unless those bronze gears just failed for some reason.

onedef92
12-19-2007, 10:32 AM
I'm trying to avoid costly issues of taking the Vette to the Vette shop here so...

I replaced the gear with a bronze one and before, it had kept grinding when you turned the motor up.
Now, when you turn the motors down, it sounds like the motor is trying to keep turning after it has already shut all the way.

Could this be a bad relay? I don't really understand electrical stuff without diagrams, so I can't pick through that info myself, haha.
It can't be the gears, unless those bronze gears just failed for some reason.

It is fairly easy to swap the actuator relays from side to side. If the symptoms change with them, then its probably the relays.

jnovak
10-16-2008, 07:52 PM
I just repaired my headlight motor, and when I plugged it in to the socket without the motor connected to the housing it simply kept running. When I pull the switch to pop up the headlights, the motor continues to spin incessantly. I was wondering if the force of turning the housing causes the motor to stop on its own, because I do not wasnt to put it all back together to undo again. Any help would be appreciated.

Hot Rod Roy
10-17-2008, 12:41 AM
I just ordered a gear set for my headlight motor. Is there anything I need to know about before I go back in and re-install? How does the motor know when to stop? I didn't notice any limit switches on this unit.

The '84-'85 (maybe '86?) headlight motors have built-in limit switches. When the headlight doors hit their stops, the motors continue to run for a little bit until the force of the motors against the worm gears pushes hard against the motor armature end play, which compresses a thrust spring. This thrust movement (about 1/4 inch) actuates the limit switch. There are two limit switches in each motor (up limit/down limit).

:buhbye: S.T.W.

remauto1100
10-17-2008, 12:49 AM
When did GM change over to the solid state box? I have a 85 and i believe the relays are mounted down in the inner front drivers side wheel well (forward side) underneath a plastic cover.... ???? I have 89 headlight system to install with module. Anyone know of a write up or diagrams to do this? Where to located the proper new harnesses.

Id be happy to give a writeup with pics when i locate the info and wiring i need. I dont really feel like digging through it all myself even though i am very capable....I am a electronic technician ya know. ...But im a lazy one...and i got interior stuff to be concentrating on right now! :laughing:

Hot Rod Roy
10-17-2008, 08:59 AM
The early style headlight motors have the manual actuation knob on the bottom of the motor. The late style motors have the manual actuation knob on the top.

:buhbye: S.T.W.

remauto1100
10-17-2008, 05:14 PM
So if i am understanding you correctly then the early style motots use the relay system and the later style use the solid state system. My 85 did not come with headlights so I acquired the late style headlights (1989 models). If all this is true then my car is a early style with relays since the plugs to the headlights are different. I know there is a complete kit to convert to later style but I dont the headlight assemblies and solid state module. I already have them. I just need the correct plug harnesses to the headlights and the module and of course the directions that come with the upgrade kits.

anthonymario
11-15-2010, 01:20 AM
My 1984 Corvette has a headlight problem one day the headlights were up I went to turn them off and they went partially down and the motors just kept running, what I did was disconnected the power and now the both headlight assemblies just rock back and forth loosely, I'm trying to figure out if it's one of the relays that is causing this, thank you very much...........