James Schulte wrote:
> Listers,
> Why would the windshield washer motor keep running when the ignition is turned
> to the on position. Only way to stop it is to pull the ground wire on it.
> Possibilities: Short in washer motor, short in harness near stalk where washer
> would be activated, bad connection at switch in stalk.
> How do I test? Using a volt meter I presume. What should I be looking for? How
> much voltage etc.
> Could it be a bad connection somewhere else in the car causing it?
> What are your thoughts and wisdom (-:
> It's a 1969 North American MGC roadster.
> Thanks in advance,
> Jim
> 69C
> 70B
>
I assume the MGB works the same as a Triumph wiper motor.
Power is always "on" at the wiper motor whenever the ignition key is on.
The wiper motor turns when it is grounded.
It is grounded when the wiper switch is turned on. The wiper motor is also
grounded inside the wiper
wear box so that the wipers continue turn after the switch is turned off until
they reach the parked
position.
The wiper motor shaft has a worm gear that drives a larger gear (maybe 2") The
wiper cable that
drives the wiper wheel boxes is attached to the perimeter on this larger gear.
As the large gear
turns the wiper cable moves left and right. Kind of like the wheels and pistons
on a steam
locomotive except the wheels (gear) is driven by the wiper motor.
Anyway, there is usually some kind on grounding device in the wiper gear box
that grounds the motor
by keeping contact with the large turning wiper gear. There is a "dead" spot on
the wiper gear that
interrupts the ground connection when the wipers are in the park position. When
you turn the wiper
switch off, the wiper motor continues to run until the grounding device (maybe
a piece of plastic
insulator) on the gear wheel touches the grounding tab. There is no longer a
ground, so the wiper
motor stops there -- in the parked position. When the wiper switch is on, the
motor continues to run
even though the grounding tab touches the "dead" spot on the gear wheel.
I would check the "ground" wire from the wiper switch to the wiper motor. If
it's grounded,
all the time, it's either a bad switch or the wire is shorted to the frame. I
suppose there could be
a short to ground inside the wiper gear box as well.
Different wiper motors implement the "ground thing" in park position in
different ways. In some of
them there is a button switch kind of deal. Something on the gear wheel passes
over the button and
interrupts the ground when the wipers are in the parked position. Maybe it's
failing "grounded" and
needs to be replaced. Number 11 in this picture.
http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29071
Looks to me like Triumph and MG used the same same wiper motors. You will see
the two different
styles in Moss and they changed from the old style to the new at about the same
time that Triumph
did (1968 or so)
Don Malling
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