Vido Peran
True Classic
Where the diodes are hidden - in vinyl sheaths
-------------------------------------------------
The diodes in the wiring to raise and lower the headlights on the
'74 X1/9 aren't neatly mounted on terminals on the back of the rotary
switch housing at the lower end of the motor and protectivelyly encased
in green sealant as on later models. Instead, they float free by their
pigtail leads as a bridge between the ends of each of two wires which
are part of the cable sheathed in black vinyl exiting from the 4-prong
connector C19 (for the left headlight) or C20 (for the right headlight)
and the terminals on the plastic block embedded in the cover plate of
the rotary switch housing.
Each tiny cylindrical diode is less than a 1/4" long and about as
wide as each color-coded multi-stranded wire. The wire carrying the
"raise" current is gray for each headlight, and the wire carrying the
"lower" current is green/black for each healight. The banded end of
each diode is on the side nearest the rotary switch, and they are
EACH CONTAINED INSIDE A SMALL BLACK VINYL SHEATH about the width of a
color-coded wire, and the sheaths extend from the end of the cable to
the plasic block. In other words, the diodes are INVISIBLE - you have
to slit the sheaths open to find the diodes. The solid wire pigtail on
the cable side of each diode is spliced directly to its cable wire,
and the solid wire pigtail on the rotary switch side of the diode is
soldered directly to a terminal on the plastic block.
In my car, the pigtail of the diode for the "lower" current broke off
at the end of the diode inside its vinyl sheath due to a combination of
corrosion and decades of cable flexing from road shock. This break could
not be seen until I slit open the vinyl sheath.
My decision to use a diode rated for 3amps (in the 1N54xx series)
turned out to be much larger than the OEM diodes and was definitely
overkill - but no harm done - and they only cost 25¢ apiece. I mounted
them on a 5-terminal terminal strip from Radio Shack. I solder-spliced
multi-stranded wire to the ends of the 2 wires from the cable and soldered
the other ends of the wire to a terminal on the strip holding the non-banded
side of a diode. From a terminal on the strip holding the banded side of
a diode, I soldered a multi-stranded wire to the terminal on the strip
and the other end to a terminal on the plastic block. The soldering job
was a mess, partially due to a need for a 3rd hand and no bench vise,
partially due to using stranded wire and no solder-sucker.
I put a some gear grease on the worm gear which turns the rotary switch
to replace the little amount which seemed to have seeped out over the decades
of use, and I smeared a thin layer of silicon sealant near the edge of cover
plate and let it dry over night to let it act as an extra layer of gasket
to aid the original paper gasket. Then I re-bolted the cover plate to the
rotary switch housing.
I attached the terminal strip to the center of the rotary switch cover
plate using a screw which APPEARS to be for putting some pressure on the
center of the rotating disc in the rotary switch. I then tested each current
path from the 4-prong connector to the plastic block, noting that current
would only pass in one direction. Then I painted all the exposed conductors
with Liquid Electrical Tape - a bad move.
I then re-installed the motor, bolting the headlight housing control
arm with the housing in the same position as when I removed it (I think),
and re-connected the ground wire and tested it, and re-connected the
4-prong connectors.
The headlight DID NOT MOVE. It used to not go down. Now it goes
neither up nor down. :-(
One possible cause is that in soldering the stranded wires to the
terminals on the plastic block, I softened the plastic enough to that
one or more of the "finger" contacts on the other side of the plastic
block which slide against the rotating metal disc got pushed back so that
the plastic re-hardened with the "fingers" no longer pushing against the
disc. I shall have to investigate this when I have the time. For now,
at least the motor is re-installed, and I can raise and lower the headlight
manually by spinning the knob. I'm easy to please. ;-)
Lessons learned
---------------
1) Clean off the entire assembly with solvent and paper towels to remove
all the grease and caked-on road grit BEFORE you open the rotary switch
housing.
2) Use a solder-sucker or solder wick to remove the solder from the
terminals of the plastic block so that attachment of the new wires
can be directly to the terminals and not to a wad of solder left on
the terminals during removal of the previous component. This will
reduce the amount of heating needed to attach and re-attach wire that
just doesn't want to grab hold of the terminal because the hole is full
of hardened solder.
3) Use solid wire, rather than multi-stranded wire. It's a lot easier to work
with for splicing and attachment to a terminal. Just leave enough length
so that the wire doesn't have to bend sharply when everything is put into
place.
4) Use a bench vise to hold the rotary switch cover plate so that the cover
plate is not resting on the bench with pressure on the "finger" contacts
underneath it when the plastic becomes softened by the hot solder.
5) Test the entire assembly for electrical continuity, including the
continuity between the "finger" contacts and the motor all the way
to the motor's ground wire, BEFORE you encase all the exposed conductors
in Liquid Electrical Tape.
The purpose of the diodes - protection
--------------------------------------
(See schematic on page 301/302 of the '74 X1/9 Workshop Manual.)
The 3 "finger" contacts in the rotary switch slide against a metal disc
which has 2 approximately 30-degree gaps which pass under the inner and
outer "finger" contacts, the gaps beginning 180 degrees apart on the face
of the disc. No gap passes under the middle "finger" contact, so it's always
in contact with the metal disc, and it connects through the headlight motor
relay coil to ground.
When the headlight switch is transitioned from the 1st to the 2nd or 3rd
positions, voltage is transmitted through fuse N to the "raise" diode, through
the outer "finger" contact, through the metal disc to the middle "finger"
contact, to the motor relay coil, and on to ground. The current through the
motor relay coil pulls the arm supplying power to the motor into contact with
the voltage transmitted through fuse B, energizing the motor to raise the
headlight housing and to turn the rotary switch disc. Eventually, the "finger"
encounters the outer 30-degree gap in the metal disc, the current is interrupted,
the relay coil is de-energized, the relay arm pops up off the power contact and
into connection with ground, stopping the motor with the headlight in the fully
raised position (if the linkage is adjusted correctly).
When the headlight switch is transitioned to the 1st position, voltage is
transmitted through fuse M to the "lower" diode, through the inner "finger"
contact to the middle "finger" contact, to the motor relay coil, and on to ground.
This leads to energizing the motor in the same direction as before, turning the
rotary switch disc in the same direction as before, to lower the headlight housing.
When the inner "finger" contact encounters the inner 30-degree gap, the motor
stops with the headlight in the fully lowered position (if the linkage is adjusted
correctly).
Through most of the operation, both "raise" and "lower" fingers are in
contact with the metal disc. But only the appropriate "finger" contact is
energized by the position of the manual headlight switch, and the inactive
"finger" contact just floats. So what are the diodes for?
My guess is that they are to block any inductively caused transient currents
from the relay coil (when it is de-energized) from pitting the associated rotary
switch "finger" contact and the leading edge of the 30-degree gap. In other words,
they are not logic components, they're protective components. And they appear
to work - the contacts in 41-year old rotary switch were amazingly clean.
VidoP
-------------------------------------------------
The diodes in the wiring to raise and lower the headlights on the
'74 X1/9 aren't neatly mounted on terminals on the back of the rotary
switch housing at the lower end of the motor and protectivelyly encased
in green sealant as on later models. Instead, they float free by their
pigtail leads as a bridge between the ends of each of two wires which
are part of the cable sheathed in black vinyl exiting from the 4-prong
connector C19 (for the left headlight) or C20 (for the right headlight)
and the terminals on the plastic block embedded in the cover plate of
the rotary switch housing.
Each tiny cylindrical diode is less than a 1/4" long and about as
wide as each color-coded multi-stranded wire. The wire carrying the
"raise" current is gray for each headlight, and the wire carrying the
"lower" current is green/black for each healight. The banded end of
each diode is on the side nearest the rotary switch, and they are
EACH CONTAINED INSIDE A SMALL BLACK VINYL SHEATH about the width of a
color-coded wire, and the sheaths extend from the end of the cable to
the plasic block. In other words, the diodes are INVISIBLE - you have
to slit the sheaths open to find the diodes. The solid wire pigtail on
the cable side of each diode is spliced directly to its cable wire,
and the solid wire pigtail on the rotary switch side of the diode is
soldered directly to a terminal on the plastic block.
In my car, the pigtail of the diode for the "lower" current broke off
at the end of the diode inside its vinyl sheath due to a combination of
corrosion and decades of cable flexing from road shock. This break could
not be seen until I slit open the vinyl sheath.
My decision to use a diode rated for 3amps (in the 1N54xx series)
turned out to be much larger than the OEM diodes and was definitely
overkill - but no harm done - and they only cost 25¢ apiece. I mounted
them on a 5-terminal terminal strip from Radio Shack. I solder-spliced
multi-stranded wire to the ends of the 2 wires from the cable and soldered
the other ends of the wire to a terminal on the strip holding the non-banded
side of a diode. From a terminal on the strip holding the banded side of
a diode, I soldered a multi-stranded wire to the terminal on the strip
and the other end to a terminal on the plastic block. The soldering job
was a mess, partially due to a need for a 3rd hand and no bench vise,
partially due to using stranded wire and no solder-sucker.
I put a some gear grease on the worm gear which turns the rotary switch
to replace the little amount which seemed to have seeped out over the decades
of use, and I smeared a thin layer of silicon sealant near the edge of cover
plate and let it dry over night to let it act as an extra layer of gasket
to aid the original paper gasket. Then I re-bolted the cover plate to the
rotary switch housing.
I attached the terminal strip to the center of the rotary switch cover
plate using a screw which APPEARS to be for putting some pressure on the
center of the rotating disc in the rotary switch. I then tested each current
path from the 4-prong connector to the plastic block, noting that current
would only pass in one direction. Then I painted all the exposed conductors
with Liquid Electrical Tape - a bad move.
I then re-installed the motor, bolting the headlight housing control
arm with the housing in the same position as when I removed it (I think),
and re-connected the ground wire and tested it, and re-connected the
4-prong connectors.
The headlight DID NOT MOVE. It used to not go down. Now it goes
neither up nor down. :-(
One possible cause is that in soldering the stranded wires to the
terminals on the plastic block, I softened the plastic enough to that
one or more of the "finger" contacts on the other side of the plastic
block which slide against the rotating metal disc got pushed back so that
the plastic re-hardened with the "fingers" no longer pushing against the
disc. I shall have to investigate this when I have the time. For now,
at least the motor is re-installed, and I can raise and lower the headlight
manually by spinning the knob. I'm easy to please. ;-)
Lessons learned
---------------
1) Clean off the entire assembly with solvent and paper towels to remove
all the grease and caked-on road grit BEFORE you open the rotary switch
housing.
2) Use a solder-sucker or solder wick to remove the solder from the
terminals of the plastic block so that attachment of the new wires
can be directly to the terminals and not to a wad of solder left on
the terminals during removal of the previous component. This will
reduce the amount of heating needed to attach and re-attach wire that
just doesn't want to grab hold of the terminal because the hole is full
of hardened solder.
3) Use solid wire, rather than multi-stranded wire. It's a lot easier to work
with for splicing and attachment to a terminal. Just leave enough length
so that the wire doesn't have to bend sharply when everything is put into
place.
4) Use a bench vise to hold the rotary switch cover plate so that the cover
plate is not resting on the bench with pressure on the "finger" contacts
underneath it when the plastic becomes softened by the hot solder.
5) Test the entire assembly for electrical continuity, including the
continuity between the "finger" contacts and the motor all the way
to the motor's ground wire, BEFORE you encase all the exposed conductors
in Liquid Electrical Tape.
The purpose of the diodes - protection
--------------------------------------
(See schematic on page 301/302 of the '74 X1/9 Workshop Manual.)
The 3 "finger" contacts in the rotary switch slide against a metal disc
which has 2 approximately 30-degree gaps which pass under the inner and
outer "finger" contacts, the gaps beginning 180 degrees apart on the face
of the disc. No gap passes under the middle "finger" contact, so it's always
in contact with the metal disc, and it connects through the headlight motor
relay coil to ground.
When the headlight switch is transitioned from the 1st to the 2nd or 3rd
positions, voltage is transmitted through fuse N to the "raise" diode, through
the outer "finger" contact, through the metal disc to the middle "finger"
contact, to the motor relay coil, and on to ground. The current through the
motor relay coil pulls the arm supplying power to the motor into contact with
the voltage transmitted through fuse B, energizing the motor to raise the
headlight housing and to turn the rotary switch disc. Eventually, the "finger"
encounters the outer 30-degree gap in the metal disc, the current is interrupted,
the relay coil is de-energized, the relay arm pops up off the power contact and
into connection with ground, stopping the motor with the headlight in the fully
raised position (if the linkage is adjusted correctly).
When the headlight switch is transitioned to the 1st position, voltage is
transmitted through fuse M to the "lower" diode, through the inner "finger"
contact to the middle "finger" contact, to the motor relay coil, and on to ground.
This leads to energizing the motor in the same direction as before, turning the
rotary switch disc in the same direction as before, to lower the headlight housing.
When the inner "finger" contact encounters the inner 30-degree gap, the motor
stops with the headlight in the fully lowered position (if the linkage is adjusted
correctly).
Through most of the operation, both "raise" and "lower" fingers are in
contact with the metal disc. But only the appropriate "finger" contact is
energized by the position of the manual headlight switch, and the inactive
"finger" contact just floats. So what are the diodes for?
My guess is that they are to block any inductively caused transient currents
from the relay coil (when it is de-energized) from pitting the associated rotary
switch "finger" contact and the leading edge of the 30-degree gap. In other words,
they are not logic components, they're protective components. And they appear
to work - the contacts in 41-year old rotary switch were amazingly clean.
VidoP
