Headlight levelling motor problem

[dorsetdave]

My 94 facelift CD Cavalier n/s levelling motor has never worked. The headlamp frame was cracked so a complete new unit was fitted. Motor still not working. Motor replaced today with a new old stock one but still no beam movement. There is a buzzing noise so power is getting through. Running the motor out of the headlamp unit shows a very small movement, say 3 or 4mm at the plastic socket . Headlamp is new GM Carello. Motors are GM 90377512. The drivers side headlight light works fine. Any thoughts? Perhaps both motors are faulty? The only one I could see on line , was secondhand and has massive stress marks on the hexagonal part of the beam adjuster knob. Looks as if it might have seized and someone was giving it help. Does anyone know where I can get one if you think that could be the problem?
Thanks for looking.

[Cavalier342]

Hmm.. Sounds strange. Have you physically put your ear close to both headlamps while getting someone to play with the leveling switch to make sure that both motors are indeed making noise? They are loud enough to be heard clearly even inside the car. I've never taken one apart but they won't require a lot of movement to adjust the beam angle, so I wouldn't expect them to move much. There is a plastic knob as well on them which you can turn by hand, I'm not sure if you need to play about with that (pardon the expression) to re-align something, hard to make suggestions really based on your message.

When you are checking the beam movement, I presume you are parked in such a way where you can see a clear line of the top of the beam pattern on a wall or some other solid surface so you can clearly gauge any movement?

[Robsey]

If the motor winds in and out by 3-4 mm, then it must be working - Electrically.

The only way for it not to move the beam angle is a fault with the basic frame set-up,

Or

The motor is not engaging properly with the beam adjuster mechanism ball joint.
------------------------------

Haynes says that motor fitting is as follows - ish...
Set the motor, so that it is fully extended.
Locate the motor onto the ball joint.
Then fit the motor to the frame and twist it anti-clockwise to lock it into the frame.

[dorsetdave]

Thanks Rob. Last night we went folk dancing and one of the other dancers there is a retired electronics engineer. He suggested plugging the two motors that are suspect into the drivers side plug. This way, the wiring being ok, will check the motors. I should have thought of that! You can hear the motor running on the nearside wiring but sometimes only for a second or two. The engineer did say that it could be an earth problem and suggested running a secondary one fron the socket. I will also check the continuity with a meter.
I have the car facing a suitable wall that I am using for beam setting.
I still have the old headlamp with the damaged bracket so can see if it is problem with the unit itself.
So that's today's task, after a small job on the Cortina Estate.
Will report with the findings.

[dorsetdave]

Sorry Cavalier 342. I've just noticed that I did not include you in my thanks. Apologies again and thanks for the suggestion.

[Robsey]

To be honest, it only takes a couple of seconds for the motor to travel the full range of adjustment.

Just checked - both motors only "share" one wire.

A brown / yellow from the beam adjuster switch.
-----------------------------
They each have their own brown wire to ground.

And they both have a yellow wire each.
These are fed by the same fuse that feeds each head lamp dipped beam.
Fuse 5 and Fuse 25
------------------------------
So you could run a link from the yellow on the faulty motor to the yellow on the dip beam wire of that headlamp assembly.

Only three wires per motor, so not a biggy to fix.

So a full fix would be -

1 - Link a fresh wire between the brown / yellow wires of both motors.

2 - Put a fresh wire between the brown on the motor and a chassis ground.

3 - Put a fresh wire between the yellow on the motor and the yellow on the headlamp dip beam connector.

It has to be one of them...

[iangsi]

Might be a silly answer but is the ball joint on the motor clipped into the socket on the reflector it takes quite a firm push for it to snap into place, you might need to take the lense off to see.

[dorsetdave]

Thanks everyone. I added a second earth to the brown cable on the plug to the back of the motor and it now works fine operating the headlamp as it should. Swopping the original motor back did not work so that motor must be duff.
So just an poor or intermittent earth, plus the one faulty motor. Two causes giving one fault.

Hope that this helps someone with a similar problem.

[Cavalier342]

Excellent, glad to hear it's sorted.

[Robsey]

Good work dear chap.

I knew it had to be something simple.
There is very little to the whole circuit.

The bit that baffles me, is how it reaches its required setting based on resistances within the switch.
I understand on modern computerised CAN controlled cars, but we are talking very old simple technology here.
I won't lose sleep over it though - as long as it works
In fact - my lights are non-adjustable.

[dorsetdave]

Rob I wondered about that as well. Not enough to cause lack of sleep though.

[Robsey]

I have sussed it out, and it is quite clever.
In simple terms.

The motors have a variable resister inside, and a comparator.
The motor actuator rod adjusts the varisble resistsnce as it moves in and out.

The switch has 4 resistors in it.
What happens is -
The beam motor comparator compares the resistance of the switch and the resistance of the variable resistor in the motor assembly.

If one is higher than the other, the motor is operated, until the resistances match.

The direction of the motor is controlled by whether the variable resistance is higher or lower than the resistor setting in the switch.

Simples.

[Cavalier342]

That would explain then why when I used to play about with the switch (because I liked the sound of the motors turning slightly resembling the electric wing flap motors on light aircraft)
when I turned the headlights off, and after a while, back on again, the motors would make a very brief sound, like re-aligning the beam, almost like a disc reader laser inside a disc drive on a Playstation console. If any of the above makes any sense at all.

[Robsey]

It makes plenty of sense.

Wing flaps and playstations.

That takes me back to 1999
(Playstation 1, version 2.. with Crash Bandicoot, Ridge Racer 4 and so on...)

[Robsey]

Here you go...
For completeness.

The Range Switch.



You can see that there are four resistors in series.
I labelled them as a, b, c and d.

The Range Motors.



The variable resistor is adjusted by the movement of the range motor, until it's resistance meets a value determined by the comparator.

As said earlier - Wiring wise, very simple.
The "little black box" (comparator) inside the range motor does the tricky / technical bit.

[dorsetdave]

Thanks for the information Rob.

[Robsey]

My pleasure as always.