|MGA turn signals have driven many people
insane. Unlike most "normal" cars, the MGA uses one or two devices that were
placed in the system to confuse the amateur. Lucas did this on purpose to try to get you
to take your car to an "authorized Lucas service representative" for repair.
Well, I am about to divulge the sacred knowledge that will allow YOU, the owner, to enter
the inner sanctum!
The first of the devices, the
one that I will discuss today, is common to all MGAs. This is the turn signal switch, the
part that lies behind the turn signal knob on the dash. If we are to use its full name,
the one that accurately describes its function, we would call it the Electropneumatic
How is it supposed to work? Well, if everything is
copacetic, the turn signals will come on when you twist the knob on the dash, and will
stay on for about 20 seconds. During that 20 seconds, the knob will slowly return to the
center position and click off. When you move the switch to activate the turn signals, you
close an electrical contact and force air out of a small chamber with a piston sealed with
a leather cup. When you let go of the switch, the spring loaded piston draws air slowly
back into the chamber through a small hole. This intake of air takes time, hence the
20-second delay before the switch clicks off. The piston turns a small cam that reopens
the electrical contact. If you take the switch apart you will see that the parts are
simpler than the explanation. More on this later.
There are only a few things that can go wrong. The most
common is that the switch clicks off right after you turn it on. There is no delay action.
The reason for this is that the air is coming back too quickly into the chamber. If you
stick your head under the dash and look at the back of the switch, you will see three wire
connections arranged around the edge of the switch. Right in the center of the back of the
switch, there is a small recessed hole. There is a small setscrew inside this hole that
controls the amount of air coming into the chamber. Take a small slotted screwdriver and
turn the setscrew in slightly, then try the switch again. Keep doing this until you get
the right amount of delay action.
What if you turn the setscrew all the way in, and there
is still no delay, or what if the screw is already turned all the way in? There is a
cotton plug behind the setscrew that acts as a bleed seal for the air, this gets hard and
non-pliable with age. The next step is to take the setscrew all the way out (careful, it's
small) and then take a small needle and tease out the cotton seal. It may be easier at
this stage to take the switch out of the dash first. When you get the cotton plug out,
knead it between your fingers until it is soft and pliable. Stuff it back in the hole, put
in the setscrew, and readjust the screw as described above.
What if there is still no delay action, or if the switch
doesn't click off? Then you'll have to take the switch out of the dash and take it apart.
When you remove the switch, note the color codes on the wires, the switch connections are
clearly marked B(attery) R(ight) and L(eft). When you get the switch out, take the three
screws out of the front of the switch and slide the plastic cover off. You will see the
metal switch contacts and the white plastic cam that activates them. To further dismantle
the switch, you will see three long screws that hold the switch together. Loosen these
carefully in stages, while holding the switch together, there may be a slight spring
tension to work against. Carefully let the switch open up, you will then see a metal
crossbar attached to the shaft, and the contoured back of the piston. The piston will
either pop out freely or will be stuck in its housing. If the piston is stuck, you may
have to pull it out with some needlenose pliers, or use air pressure through the setscrew
hole. There is a spring behind the piston, don't lose it.
Once the piston is out, remove all the 30-year old grease
with some alcohol or Trichloroethane based brake cleaner. DO NOT use carb cleaner, or you
will damage the plastic. Fold out the edge of the leather seal and relubricate everything
with Vaseline or white lithium grease, then reassemble the switch. If the switch still
will not stay on for 20 seconds, try wrapping a turn of masking tape around the barrel,
under the leather seal. This will effectively increase the pressure of the leather against
the wall of the switch.
Before reinstalling the plastic cover, you may want to
clean up the switch contacts with fine sandpaper. Don't forget to readjust the setscrew at
the back for the proper delay time. Now you are ready to reinstall the switch in the car,
and you have saved yourself 150 bucks for a new switch.