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b85 308 headlight problem

2394 Views 6 Replies 0 Participants Last post by  Bill Van Dyne
The passenger side headlamp on

The passenger side headlamp on my 308 suddenly won't raise when I turn on the switch. The driver side is fine. So far, I've switched the relays, replaced the fuse, cleaned the connections at the fuse/relay box, retightened the ground wire at the lift motor, and checked for juice. I found juice at one wire at the white connector near the motor, but none at the wires of the black connector, with the switch in the on position. Is this correct?
In another thread , it was mentioned that there are diodes in the motor. Where are they located and how do I get to them, test them, or replace them? Any other ideas of what might be wrong here? Is there another ground wire for the motor or is there just the one on the sie of the motor? Any help, tips, suggestions,would be most appreciated.
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Hi Bill:

Shown below is a p

Hi Bill:

Shown below is a proceeedure written by Ric Rainbolt that I used to check the diodes in my headlight lifting motor. In my case one of the diodes was bad. It was a simple matter of removing the motor, cutting and pealing back the rubber covering and sodering in new diodes. Hope this helps.

Ric's proceedure:

You can check the diodes in the headlamp lifter motor without removing the motors from the car. You'll need a multi-meter (VOM) that is capable of checking diodes (preferred) or one that has an low resistance Ohms range. Also needed are some screwdrivers and possibly end wrenches (10mm) and a low-wattage soldering iron.

This procedure is for 308's, specifically my '81 308 2-valve. Other models and/or years may vary, but I think its the same all the way through the 328 model. GT/4's and 246's may be similar.

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 woodburning) 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).
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Hi Bill, of the

Hi Bill, of the first things that should always be checked after fuses, relays, etc. of course is the tightness of the nut & linkage arm on the side of the motor. These have a habit of working loose over time.

Easy to check by opening the hood, turning the thumbwheel on top of the problem motor while watching the lifting lever arm. If while turning the light doesn't lift, turn it back and tighten the 10mm nut, they try the lights. Be careful when using the thumbwheels with the battery connected, as the motors can quickly spin on their own at a certian point in the travel.

Regards, JRV
Thanks for the extensive reply

Thanks for the extensive reply, Drew--I'll download this for futire reference.

JRV--you've done it again, Man. It was nothing but the loosened nut which you suggested I look for. Sure enough, it was loose as a goose--after tightening it back up, everything resumed perfect working order. Thanks, again, my friend--again, you've saved me a lot of work and fretting.
Great tip JRV, I hadn't he

Great tip JRV, I hadn't heard that one, but most of my friends that had the "diode problem", had slightly different symptom; the light mechanism would usually move a little or even "wink", then stay closed.
>>you've saved me

>>you've saved me a lot of work and fretting.<,

Well good our mission statement is being fullfilled.

BTW Bill, no need to frett as long as you have Ferrari-Talk on your side...
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Amen, JRV--thanks, again.

Amen, JRV--thanks, again.
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