Headlight Motors

General Information

Info - 84-86 models

All 1984-1986 model Fieros use a similar headlight system to the 1982-1986 Firebirds. There are two motors, and three relays in the system. Here's how it works:

Here's more than you ever wanted to know about the headlight door circuitry for the older cars which use relays in lieu of electronic controls. Sorry about the bandwidth, but there's no easy way to say it. Hope it helps someone.

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 which 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:


        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: $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, than 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 Pontiac changed to electronic (as opposed to electro-mechanical) controls.

From: Harold

Info - 87-88 models

The 1987-1988 Fieros use a new headlight system, which is also used in 1987 and later Firebirds. This system has two motors and an electronic module which controls their operation. Here's how it works:

There are only two wires connected on each motor. Green(/black) and grey(black), and they connect to the output (4-pin connector) on the headlight control module. The other connector (5-pin) on the module is the inputs. The two red wires are the continuous power from the battery through two fusible links, as in the 84-86 system. The white and yellow wires from the headlight switch are also the same, as is the ground.

Everything on this system is done inside that little electronic control module. When the headlight switch is on, it trys to run the headlight motors in the up direction. When it is off, it tries to run them in the down position. Rather than having seperate wires for each (and ground), as the previous system did, this one reverses the flow of current across the wires to turn the motor in the opposite direction. Also, rather than having an internal limit switch inside the motor, the control module actually senses the current being used by the headlights. When there is a sudden rise in current draw, as happens when the motors can no longer turn, the module shuts off the power to the motors.

Internally, the main difference between the new motors and the old ones (other than the fact that the current sensing mechanism is now located in the control module rather than the motor), is that the new ones are designed so that rather than stripping out the gears that drive the motor, they have a bushing which will break. They are bolted together, rather than riveted like the older ones, so that this bushing can be easily replaced.

From: Sketch


Common Causes of problems

[Note: this is obviously intended for 84-86 models, but some of it applies to all years.]

(From five page article in January 1990 Super Automotive Service)

Fiero Headlight Door Symptoms/Causes

From: Scott Backer

Testing - 84-86 models

If the headlight motor (actuator) KEEPS RUNNING, it's the actuator - or more precisely, a worn out gear on the clutch mechanism at the bottom of the actuator. New actuators cost $160/each (list). The right one (on an 84) is GM Part # 22039673 and the left one is GM Part # 22039672. You might be able to find a used one at a junk yard for $50-$75. But I would spend the money and get a new one. This way you won't have to worry about it for quite a while. If you are mechanically inclined you should be able to change one in 30 minutes with just a couple of sockets (13mm for headlight assembly nuts and a 10 mm for the long actuator to headlight assembly bolts). Just remember to disconnect power first and crank the actuator up and down by hand. Remove the entire assembly (4 nuts), then remove the actuator (3 LONG screws and one nut on the lever arm). Installation is just the reverse.

If the motor NEVER comes on, I'd say it could be either a bad relay or the motor brush/switch assembly is dirty or shot (this can be replaced separately. It's GM Part # 22038870 - list is about $30). If the motor doesn't come on (won't go up/down) I'd try this:

  1. turn the lights on to try to bring the headlight up.
  2. With the light switch still in the on position, open the hood and bring the defective headlight up by hand by turning the knob on top of the actuator. Don't force it. It should turn pretty easily. The action of turning the shaft might be enough to get it started.
  3. If 1 & 2 fail, try swapping the right and left headlight relays. BE CAREFULL! There are three relays used for headlight operation. There is an isolation relay mounted on the left cowling, and two headlight relays. The right headlight relay is mounted just to the left (inboard) of the right headlight assembly (between the headlight and the coolant overflow bottle). The left headlight relay is mounted just to the right (inboard) of the left headlight assembly. DON'T swap a headlight relay with the isolation relay (which is mounted to the left (outside) of the left headlight assembly. If you swap headlight relays and the problem switches sides, it's the relay.

If this doesn't fix your problem you either have a bad wire (really unlikely looking at the schematics), bad actuator motor (burned out contacts or winding), or bad isolation relay.

From: Bill Salina


Fixing the motors

On the 84-86's, the gear becomes stripped, and there's a guy in Florida who makes replacement gears out of bronze which he sells for $50 each.

On the 87-88 system, there is a bushing that wears out. You can get a rebuild kit with the bushing from Ecklers Corvette (mail order place out of Titusville, FL. Phone number: 1-800-327-4868) for about $5. The part number is E-29304. The Corvette headlight motors use the same bushing.

From: Sketch

Swapping Motors

A knowledgeable proprietor of a Firebird performance scrap yard clued me in that mid-80's (82-86) Firebird headlight motors are interchangeable with early Fiero headlight motors (84-86) with one note:

the right and left motors are switched ie. the driver's side motor on a Firebird matches the passenger side motor on a Fiero. I cannabalized the Firebird motors for their gears and they work perfectly. If you do likewise, replace both gears -- not just the broken gear -- as there are differences in gear pattern. The Firebird motors appear to be entirely interchangeable with the Fiero motors, but they need to be internally inspected and regreased to ensure they aren't subject to the same grease coagulation / broken gear problem as the Fiero motors you're replacing.

As there are so many more Firebirds out there, parts may be more available and less expensive then Fieros.

From: Terry Leftgoff (c/o Nick Varetakis)

If you find and 87 or 88 Fiero in a junkyard, you can (relatively) easily convert your headlights over to the new system. This requires changing the entire front wiring harness. Remove it where it connects to the bulkhead near the power brake booster, and disconnect the wires from the windshield washer pump. Move to the front (headlight area), and you will have to remove a lot of wire holders, and electrical connectors on all of the lights and the coolant fan motor. Remove the headlight motors, and the control module, which is located on the outside of the frame, just below the driver's side ront marker light (in front of the wheel well). You will also need the coolant fan relay (in front of the driver's side headlight), because it has a different connector from the one used on older Fieros. Now take all of that, and put it in your car. Instant (well, almost) 87-88 style headlights.

On the other hand, if you're handy with a soldering iron, you could just take the motors and control module, and wire it up to your existing system. If you do this, you could use the motors and control module from an 87 or later Firebird instead (may be easier to find).

I did this on my car, and here is the schematic for the headlight wiring which is now on my car. The original wiring is on the left, and the new wiring is on the right. The "dots" are the points at which I soldered the wires together. Email me if you need more information.

From: Sketch

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