So your Fiero is winking at you or you shutdown to find something whirring that just won't stop ? If that's your problem, you're not alone, at one time or another nearly every Fiero owner has faced a Motor Failure (MF).
This helped me when I purchased my latest toy at a municipal auction (same way the Blues Brothers bought their Dodge), as soon as the battery was connected, the whirring began ond only quit when the battery was disconnected. Knew what it was and was not particularly bothered but did keep the bidding down.
Now one answer is a new headlamp motor but they are kind of pricey. Or you can try to fix it yourself for 99 cents (plus tax). Did this with my '84 once and have now gone through both in the '86. The second time I had my trusty Kodac DC-20 out and this is the result. Look at it this way, you won't hurt anything that wasn't already broke.(Note: this works for 84-86 Fiero and 82-86 Firebird motors. It may work on 87-88 but have not had one. Yet.
I assume you have have already disconnected the battery to stop the motor from spinning. If not carefully disconnect blue connector and the power wires from the relay. Despite what you might think from reading the manual, just disconnecting the blue wire will not keep the motor from starting, it will just keep the lights from going DOWN. If DOWN they will still try to go UP when the headlamps are turned on, they will just stay up once there. Once the main power connector (with the red/pink wires) is disconnected from the relay, it cannot do anything.
Is a good idea to find this connector and practice removing it a few times so you can do it when the motor is going berserk at night at the 7-11. Looking forward from the back of the car this is on the passenger side of the relay and there is a tab you push on the side of the connector while pulling down (actually removing either set of wires - the motor leads are a near identical connector on the other side of the relay - will depower the actuator, the power leads just need to be removed before pulling the bucket). Naturally they are both on the bottom so you cannot see either yet, you just have to know.
Before you start it would be a good idea to line up the items you will need: quarter inch rachet with 7, 10, & 11 mm sockets (can be deep or not) and a three inch extension (more or less). flat screwdriver, small pliers or needlenose, electric drill with at least one drill around 3/16"-1/4". Glob of axle grease, some paper towels, a newspaper, ballpoint pen, and eight 6-32x1/2" long screws and nuts (pack of 10 in brass is 99 cents at K-Mart).
OK the power is off and the bonnet is up. Blue lead and relay power is disconnected. The next obstacle is to remove the headlamp assembly. The good news is there are only four nuts/washers you must remove. The bad news is that you can only see two. Worse, the headlight needs to be up to get to reach the other two nuts and down to remove the bucket so get out the pen. First loosen but do not remove the top two nuts with the 10 mm socket. This relieves pressure on the bottom two. Next, gently lift the headlamp. Hopefully it will just come up partway and stop. Get out the pen and use it to rotate the motor clockwise in the direction of the "OPEN" arrow. You will need to twirl for a while but be patent. It might just flop open and not stay up. In this case you will have to prop it up.
Now you had best use the extension to find the two nuts on the bottom. Remove them. Now they are just in rather large slots (why they need the big washers). So in theory you can just loosen them, crank the headlamp down, remove the top two and pull the bucket. In practise I always wind up having to remove all four so you might as well.
When the bottom nuts are removed, crank the motor counterclockwise to lower the headlamp then remove the top nuts. You should now be able to remove the headlamp bucket assembly. To get around the lid prop on the driver's side, you will probably need to rotate the unit toward the passenger side. If you did not crank it down all the way first, you will now find out why you should have.
Remove the entire assembly and put it on top of the newspaper on a flat level surface (card table and chair is best). Find the C-clip holding the headlamp arm to the motor arm and remove it. If it lifts off easily, do so. If it binds, wait until the three motor bolts are removed.
Either remove the motor connector from the relay or unbolt the relay bracket (7 mm socket) and set aside. Unbolt (10 mm socket) the three long bolts holding the motor to the bucket. Note that the middle one is shorter than the others. Remove the motor from the bucket also removing the headlamp arm if not already done. Set the bucket aside
First use the 11 mm socket to remove the silver nut from the shaft. Make a note of which way the arm is pointing (should be in the region of the switch cover held on with three screws). Wiggle the shaft to remove from the shaft. If stuck, it may be necessary to use some WD-40 or equivalent and a vice & drift but is easiest to remove while motor is still riveted together.
The next step is to drill out the eight rivets around the edge of the motor. Do this somewhere that the metal chips can be collected and wear protective glasses. The size of the drill really does not matter so long as it is larger than the rivet body (about 3/16"). You will notice that each rivet has a domes end and a concave one - it is easier to drill the concave one. You do not have to drill very deep - about 1/16" - or just enough so the rivet head comes off. You will feel a slight pop when this happens and sometimes the head will start spinning on the drill.
Push each rivet body out of the motor using a nail or jewlers screwdriver. Do not pound with a hammer as it is easy to break the case - if the head is removed properly, the rivet will just push out.
Being gentle, use the flat screwdriver to pry the case apart. Wiggling may be required. Keep the deeper half with the etended shaft on the bottom. Note that there is probably some RTV sealant between the case halves that may need to ne sliced.
Once the case is separated, there will probably be a green substance that has the appearance of wax, soap granuals, or even molded plastic. This is what used to be the lubricant but is now clogging the works. Dump this out somewhere taking care that the gears and armature do not fall out.
Next remove the plastic drive wheel and shaft with its metal insert noting which way it is pointed because you will want to replace it after turning 180 degrees. If the gear teeth and crossbars that retain the steel assembly are in good shape you are in luck. Even if not. I have had good luck replacing it 180 degrees out so that different teeth take the start/stop loads where it usually fails. More later.
Remove the steel gear taking care to note the wavy washer on one end. Check the large portion for the green stuff clogging the teeth. This will force the worm gear out of engagement so the motor just spins without turning the gear. Hopefully just removing this will restore the unit. I generally use a steel brush to clean the teeth though a small screwdriver whose blade will fit between the teeth will also work. Clean the helical gear that engages the nylon gear also.
Clean around the armature as well and remove all of the old grease. You should not need to remove the armature to do this but if it does come out, be very careful to note which side of the steel magnet assembly around the armature coils faces out. Get this wrong side out and the headlamp will operate backwards (if you need to replace an armature, this is how to reverse it).
For those interested, the motor is powered all of the time, either open or close. ON/OFF is achieved with a spring and the two silver plates between the coil and the worm gear bushing on the armature. The two plates each has a rod on the side you cannot see without removing that extends into the area under the switch cover. This has two spring-loaded contacts in it.
The external relay applies one polarity if the headlamps are on and the opposite if off. This turns the motor on either forward or reversed. When the limit is reached, contact with the stop puts excess back pressure on the motor, stopping the gears and the worm tries to climb the gear. This moves the armature either up or down and the levers on the silver plates open the respective internal switch, stopping the motor. This is why the motor runs continuously when clogged - either up or down - because it never generates enough force to activate the switch.
Once all parts are cleaned and the green gunk removed, reassemble. I use regular axle or ball joint grease. Coat each rotating element and fill the cavity above the armature shaft. A dab on the shaft by the knob will not hurt, these are all plain bearings, some to plastic. Remember to reinstall the nylon gear rotated 180 degrees from original. The arm will fit on either way.
The factory used some RTV to seal the case but I generally do not bother - the grove/raised surface will seal well and there is a 1/8"x1/4" opening at the end of the armature so will never be airtight. You might want to re-grease in a decade or so anyway.
Once the cases are together snugly, use the eight 6-32x1/2" (if you can't find 1/2", 3/4" will work) screws and nuts in the same places the rivets were to hold the case together. Snug tightly with the screwdriver.
Use the 11 mm socket to reattach the arm to the motor and snug tightly again. If in doubt about where it stated, point toward the bottom of the switch cover as in figure 8. Rotate the knob to line it up. Don't play Godzilla, the nylon gear is all that is holding it inside. Note that the steel/nylon assembly allows the arm to move relatively freely in about a 30 degree arc. This is normal.
From here, reassembly is a simple reverse of disassembly. You may want to attach the headlamp lever to the arm with the C-clip before tightening the three mounting bolts. Be sure the arm/lever orientation is the same as when you started. Remount the relay if removed.
When putting the bucket in the car, take care that none of the wires get trapped between it and the body. If the lower nuts cannot start the blue wire connector is probably trapped.
When ready, carefully connect the power wires to the relay with the headlamps OFF and UP (keep out of the way just in case something is RONG as in the note below). Turn the headlamp switch ON and both lamps should come on. The other will go up. The one you are working on may come up a bit so keep hands away. Now connect the blue wire then thurn the headlamps OFF. Both should go down. Try again and both should operate.
Note: If the headlight goes up when the headlamps are turned OFF and down when turned ON, the armature magnet is upside down and everything will have to come apart again. Check twice before reassembling.
Earlier I mentioned rotating the plastic gear. Some say this will not work, others such as Bart Waclawik - a source for gears say it won't work for long. On my '84, it kept one motor working for over two years (was working when sold). My take is that if you need a gear this will keep it working while you order a replacement provided it is not really bad. In any case you are only out about 20 minutes time and it may last a while.