Diode location Headlamp motor .... Please!

Discussion in 'Technical Q&A' started by Dino355, Jan 29, 2008.

  1. Dino355

    Dino355 Rookie

    Nov 5, 2007
    Wimbledon England
    Full Name:
    I think I have traced the stuck up headlight to a diode problem this being the case without a doubt from all of the help I have received here, thank you.

    The only question that I have now is where is the little chap located and how is it changed or is a new diode just fitted in line and if so in which wire and which direction??

    Oh and the winning lottery numbers would be fab too! not asking to much am I .... Love you!

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  3. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    Full Name:
    Hugh G. Rection
    Dean, my understanding from reading other threads on the subject is the diodes are hidden under that thick gray vinyl coating that has been sprayed on the entire outside of the motor assembly. Search the archives and you should find threads on removal of the motor, and careful surgery of the outside to find and replace the inexpensive diodes.
  4. Drew Altemara

    Drew Altemara Formula 3

    Feb 11, 2002
    Tuscaloosa, AL
    Full Name:
    Drew Altemara
    #3 Drew Altemara, Jan 29, 2008
    Last edited by a moderator: Sep 7, 2017
    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.


    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 .


    Drew Altemara
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  5. bowbells

    bowbells Formula Junior

    Jan 14, 2008
    Full Name:
    Arthur Dent
    The lights are operated via 3 relays, I find that typically one of those is bad. The lift motors shoiuld both be hooked up when checking. Without a wiring schematic (even with one as well) it is not easy to figure out problems.

  6. Dino355

    Dino355 Rookie

    Nov 5, 2007
    Wimbledon England
    Full Name:
    Again many thanks for the quick reply, I would assume that if you can measure the diode from the plugs that connect to the motor you should be able to fit a new diode IN LINE at this point even if this was only just to confirm if this is problem. I was thinking about soldering a wire to each end of a diode and then connecting it in line on a temp basis just to see it the motor would go down.

    This may take a few tries to get it right and you could house the new diode in a fuse connector if it worked out ok on a permanant basis with no need to even remove the motor. All appears to be a good idea unless YOU know differently

    Interestingly when I had both plugs undone I cross connected the grey to black and the motor went into a cyclic motion and went up and down non stop, bit of a panic but to me this did as least prove that the motor could also go down as well as up so the motor part should not be faulty?????

    Any ideas or warnings would be appreciated also if all fails detail of how to remove the headlight for dummiesfor be gud!


    Wobbly eye 355
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  8. Dino355

    Dino355 Rookie

    Nov 5, 2007
    Wimbledon England
    Full Name:

    Fantastic! And with the picture of the diode's on the motor I can now see why they need to be replaced on the motor and in line would not help...

    Again many thanks you are a true gentleman and I do appreciate your time sir!

  9. Llenroc

    Llenroc F1 Rookie
    Rossa Subscribed Consultant

    Jun 9, 2004
    Full Name:
    Great write up Drew, thanks for taking the time.
  10. f355spider

    f355spider F1 World Champ
    Rossa Subscribed Owner

    May 29, 2001
    Full Name:
    Hugh G. Rection
    Indeed, a "keeper"!
  11. jeffdavison

    jeffdavison F1 Rookie
    Silver Subscribed

    Jul 29, 2002
    Suwanee Georgia
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    Jeffrey Davison
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  13. Big N

    Big N Karting

    Jul 30, 2008
    Dublin, Ireland
    Full Name:
    Hi All,

    Does anybody have any idea what value the diode in the Headlamp motor is?

    Tried searching but no doubt its on the forum somewhere,
    All help greatly appreciated.

    Many thanks
  14. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    Steve Magnusson
    #11 Steve Magnusson, Jul 10, 2009
    Last edited: Jul 10, 2009
    See point 10 in Drew's post #3 in this thread for Ric Rainbolt's prior recommendation.
  15. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    Read Drew's good writeup or the Theory of Operation below
    I just posted this in the 400 forum -

    Diodes are power not signal diodes. Diode characteristics are NOT critical
    Use 1N4001 diodes or equiv.
    1N400x series diodes are all 1A forward current. but the last number is Peak Inverse Voltage.
    Bigger numbers mean higher PIV and lower reliability - 1N4002=100V is OK. Going overboard -1N4007=1000v is not.

    Theory of Operation
    A set of contacts w/diodes at the lift motor detects when the headlight lift assembly is fully up or fully down.
    If not, contacts sends this low level information to a related relay coil which sends voltage to the headlight motor.
    The diodes allow some common wires side-side while isolating one side from the other.
    The only current involved in the detection circuit is a very low relay coil current.
    These diodes rarely go bad as this circuit which places low demand on the diodes.
    For any of them to go bad relates more to the vibration environment than the electrical environment.
    If one diode does go bad, there is no reason to replace any others.

    Virtually all Ferrari movable headlights in from 1970 to 2000 use this same circuit and components.

    Reply With Quote
  16. Pantera1523

    Pantera1523 Formula Junior

    Mar 17, 2004
    Full Name:
    Scott Carpenter
    Ok so I just got back from a 400 mile drive and have problem with my headlights...

    The drivers side light seems to only want to be in the half open position. If I turn the lights on at the stalk both will raise, the passenger one will stay up. The drivers side one will close (from a partially open position) then open all the way and then come to rest back in the partially open position. The headlight is on so I have that going for me...

    I should mention here that when I first looked into the headlight motor area there was a black wire that had come loose. I assume it was a ground wire so I reattached it to the open spade connector that I found in the vicinity.

    Using the above steps I got as far as turning on the lights then turning the knob on the motor to see if I can raise the light into the proper position. This started to work but then I must have hit a limit somewhere and it quickly raised and lowered on its own scaring the bejeesus out of me. ;)

    So my question is this.. do I have a diode problem as described above? Or is mine just somehow out of alignment and it needs to be reset somehow?

  17. Pantera1523

    Pantera1523 Formula Junior

    Mar 17, 2004
    Full Name:
    Scott Carpenter
    #14 Pantera1523, May 6, 2010
    Last edited by a moderator: Sep 7, 2017
  18. spiderscott

    spiderscott Formula 3

    Feb 24, 2004
    Ratarossa HQ UK
    Full Name:
    Hi all, I have a strange problem with my LHS headlight motor on a 355. Don't think its any of the above symptoms.

    When I turn the lights on the RHS pops up normal, but the hand turnable wheel on top off the LHS motor just spins fast i.e the motor is spinning up trying to life the headlight. if I then give the headlight assy a helping hand and start to assist lifting, the motor bits and completes the lift, turn it off and on again and it does exactly the same.

    Im suspecting possibly a worn gear inside with tooth missing ?

    My question is, can and if so how can you get into these things and take a look at the workings ? I took two allen bolts out that I could see under the mass of grey protecting paint but could not figure any further how to split the assy apart ?
  19. Qavion

    Qavion F1 Rookie
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    Feb 20, 2015
    Full Name:
    Ian Riddell

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