How to get to the fusebox (456 GTA)

Pull the upper lip of the carpet towards you and you will find two M6 screws that hold the door to the fusebox.

 

If both lights go up, it's not the fuse. There may be a chance it's a relay. There are 3 relays for headlight pod motors and control.
I don't have manual for the early cars to know if the relays are the same, but on an "M" car, because both headlights are affected, relay D could be faulty.

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Swap relays D and E (or their equivalent on the 456). If relay D was faulty, one of the headlights may not work, but the other one should go up and down.

 

Interesting. Usually it's not a relay if it goes half way up, but it seems like the relay swap worked. I'm looking forward to seeing what the new relays do.

 

Interesting. I don't know if you have one problem or two. There are numerous possibilities.

The left headlight problem could be:

Broken plastic gears inside the headlight motor/gearbox
Corrosion on the metal disk inside the gearbox.

The right headlight problem could be:

Blown diode on the "down" circuit
Corrosion on the pins on the motor/gearbox connector

Generally, pod mechanical linkage adjustments can cause problems. Dried up lubricant inside the gearbox can create problems, too.

I'm just surprised you have two problems at the same time. Depending on your skill levels, I would suggest either taking the car to an autoelectrician (who has a wiring diagram for the 456) or doing electrical checks/pulling the headlight assemblies to pieces. Basic maintenance like cleaning the pins and sockets on the wiring connectors shouldn't be too difficult. I could send you the wiring diagram for the 456M and hope the headlight circuit is the same on the 456. Are you in Europe, the USA or elsewhere?

 

Just to reduce the amount of options, you may try the functions of the motors themselves first; if you rotate the knob at the top of the motor (hidden under a black cover) by hand, you will see the lamp start moving. Then, all of a sudden, the motor takes over and performs a cycle. If this doesn't happen look at the motors first. They can be rebuilt as shown here on this forum.

 

I'm not familiar with the electrical connectors on the 456 headlight motor/gearboxes. Some schematics show an 8 pin connector (5 contacts used), but this doesn't match photographs.

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Are the circular metal rings electrical sockets? If so, are the 2 lower ones for the motor and the 3 upper ones for motor control?

 

Wiring in the headlight motors:

 

By "motor" do you mean the motor itself... or the whole assembly (motor, gearbox and diodes)?

I believe the metal disk (shown in your diagram) rotates 180 degrees for up and 180 degrees for down (in the same direction). If a headlight pod goes up (easily), but not down, it does sound like a diode or perhaps the broken finger (floating contact) attached to the red wire or, less likely, some corrosion on the disk just beyond the half way point. If you turn off the headlights and rotate the knob manually to lower the headlight (in the same direction as the knob turned with electric power) and electric power doesn't take over manual movement, it could be the diodes or a broken finger, but it's unlikely to be the motor itself.

I would take power off the headlight pods and manually operate both headlight pods through complete cyles to see if the movement is smooth. This should eliminate gearbox plastic tooth problems and, perhaps, misadjusted linkages.

 

In one of my motors the metal disk was partly corroded, making intermittent contact. It's difficult to understand why they used polished steel, not brass, for that disk. Also, the ground wire (brown) was poorly connected.