from this link: LINK
A Picture and a Thousand Words:
This is for older cars than yours but I think the principal is the same and location of the diodes should be similar.
TROUBLE SHOOTING POP UP HEADLIGHTS
Pop up headlights are used on a number of Ferrari's. I have owned 308's, a Daytona and a Boxer and they all have the same basic system. I thought it would be of potential benefit to describe this system and run through the problems that can occur and their potential cure.
The System Is Not That Complex
The basic system itself is not that complex, but like Ferraris there are a lot of electrical and mechanical parts to go wrong. The system utilizes a switch to activate a relay that provides power to the headlight lift motor. The lift motor itself employs a cam system and two diodes to sense how far to rotate the cam, clockwise or counterclockwise. The cam has a gear attached that moves a rod to open or close the lights.
The Quick Fix
A lot of times the rod that is attached to the cam gear has come loose. You turn the light switch and just one light goes up. First thing to do is check that the nut that attaches the rod to the gear has not come loose. Sometimes just tightening this solves the problem. It can also happen that if this nut is loose and then retightens 180 degrees out of phase the headlights can "wink". In the off position the headlight is up and vice-versa. Check the securing nut first. This can be the issue more times than you think.
A Little Deeper: One light will not activate.
First thing to do is "The Quick Fix". But if this does not get it we have to dig a little deeper. If one light operates odds are the problem is not with the switch in the steering column stalk. The first thing to do is to check the fuse panel. Most of these cars have separate fuses for left and right lifting motors. Rotate them and see if that makes a difference. If not time to move on the relays. There are separate relays for the left and right lifting mechanisms. The first thing to do is to rotate them to see if that makes a difference. If not time to move to the lift motors themselves.
The next thing I generally do is to check the wiring leading to the lift motors. The plug to the motor is four prong. The wiring runs from the relays to the RHS lifting motor and from there to the LHS lifting motor. With a volt meter ground the black post and measure 12 V, plus or minus, on the wiring leads to the good motor. Take measurements with the steering column stock switch in the on and off position. You will have 8 readings (4 prongs x 2 positions). Record the information and compare it to the "bad" side. The measurements should match for each colored wire. For instance, in the on position, with the black/negative post grounded and the red lead on the green/black wire on the "good" side recorded +12.5V. This should be the same as the green/black wire on the offending side. Some measurements will be zero. If there is a difference odds are there is a short in the wiring running between the two sides.
Ok what if everything has checked out so far.
Time to move on to the motor. There are two ways to trouble shoot this.
First a word of caution: The motors have round knobs on their tops to allow you to raise and lower them in manual modes. However if the steering column light switch is in the off position an attempt to raise a good lifting light motor will cause the motor to activate, raise all the way and then lower itself. This can happen in the offending motor also. Don't get you fingers caught in this, please.
With the stalk in the on position, manually try to raise the offending motor by turning the knob on top of the motor. Remember the caution above. If it raises then lowers automatically, but will not stay in the up position at least we know the motor is working, all-be-it not properly.
Pull the offending motor. The problem is probably with the motor itself or the diodes. The next step is to take the motor over to the good side, disconnect the wiring harness from the good side and plug in the problem motor. Turn the stalk to the on and off position and watch the rotation of the gear if any. Did it actuate? Did it behave the same as when it was wired in to the "bad" side? If so, we have confirmed a motor problem.
At this point it is my recommendation to check the diodes in the motor. They are located on the outside of the motor housing but are covered by a black rubbery material. There are two of them. Fortunately we can test these with a VOM meter by testing the wiring harness leading to the motor.
A brief note, this test can be done out of sequence from the above to diagnose a problem diode on a lift motor to speed up the process.
Shown below is the procedure which I have copied from a previous write-up by Ric Rainbolt
1) Disconnect the battery ground strap.
2) The headlamp motors connectors (both sides) should be disconnected. You probably will need to remove the grill (308's) or cover (328's) above the headlamp mechanisms to accomplish this, or, if you're flexible and nimble, you may be able to reach it with just the front bonnet up.
3) Use the hand crank knob on top of the motor to move the headlamp to about the halfway point (i.e. 1/2 up, 1/2 down). No precision is needed, just somewhere in between.
4) Now use the VOM to check the diodes by measuring the conductivity on the BLACK and GREY terminals. Measure with the VOM and then reverse the VOM leads and measure again.
If you have a VOM with a diode check feature, in one direction you'll get infinity (no reading) and in the other you'll get a low value (usually less than 1.00 V).
If you're using a VOM in Ohms mode, select a low scale range (1-3K ohms). In one direction you should get a low reading and in the other a fairly high or infinite reading.
5) Now check the other diode by measuring, as in step 4, with the BLACK and GREEN+BLACK wires. Note that at this point, both diodes share the BLACK wire.
6) If all is well, you should have made four measurements. Two will show a low value and two a high (or infinite) value. If any pair shows low values in both directions, the diode is shorted out and needs to be replaced. If any pair shows high values in both directions, the diode is "blown" and needs to be replaced.
7) If either diode is bad, you'll need to remove the motor from the car. This can be done by removing the drive lever nut and the drive lever and then the three bolts that hold the motor to the headlamp lifter assembly.
8) Peel back the rubber covers on the motor. This can be tough, but it can be done. Only the lower cover needs to be removed.
9) On the lower part of the mechanism, below the motor on the gear housing, you'll find a pair of diode rectifiers (small cylinders, usually black with a white or silver stripe at one end, with two metal leads coming out). Using a low-wattage soldering iron (designed for electronics, not wood burning) and remove the offending diode. Make sure to note the orientation of the diode before removing it. If you don't know which one is which, measure the diodes again with the VOM, this time directly on the diodes leads.
10) Take the dead rectifier to your local friendly electronics parts store (Radio Shack or equivalent) and find a similar sized unit from their stock. Exact specs are not really critical as all the part is only used for is to rectify a signal to a relay. Find a rectifier with at least a 1 Amp rating and a minimum of 50V. A "1N4001" is a good choice.
11) Put the good rectifier on the motor and perform steps 4-6 again. If all is well, reseal and return the lifter motor to the car.
12) Reconnect the connectors and the battery ground strap and test. Be careful when you reconnect the ground strap, since the half open headlamps will most likely cycle back to the resting position... don't be in the way when this happens, the car could get scratched or it could bite off your fingertips.
NOTE: Measure both headlamp lifter motor's diodes. Sometimes, a diode failure in one motor can cause the opposite headlamp to act up (no really).
If the diodes check out OK and the motor will not actuate odds are that the motor itself is "kaput". Call your local Ferrari parts supplier and order the motor. Motors, though similar through Ferrari models, are slightly different and you must specify LHS or RHS.
What If My Headlights "WINK" OR CYCLE?
Some times one or both of the lights will wink or cycle when the lights are turned on. One light comes up, goes down and comes up to stay or runs continuously. Odds are high you have a diode problem. Perform the diode test on the offending motor.
What if both lights will not rise?
My suggestion here is to check the fuse/fuses (some cars may pass both lifting motor current through one fuse), check the relays (rotate one of the lifting motor relays with a similar one on the circuit board - they are numbered), perform the wiring harness test at the motor, do the diode test.
If no dice, the problem may be in the steering column stalk switch. A real PITA.
I think the above should handle the majority of problems that occur with Ferrari pop up headlights. I don't have any expertise removing, trouble shooting and replacing the steering column stalk switch. Perhaps in the future another contributor can explore this area. But I sure hope that is not me .