Connected directly to the battery the motor should just run. Connected
through the switched supply and the correct relay the motor will run at the
required rate. Oscillation of the wiper is generally by mechanical means
rather than switching the supply polarity (someone correct me if I am
wrong). Are you sure that the relay hasn't failed?
How are you not sure if it works? It either works, or doesn't.
You can check the supply with a 12V test lamp/bulb.
Sometimes, if it's a hatchback, there are a set of tailgate
spring loaded contacts, these can oxidise/corrode.
Sometimes the motor has three supply wires, one +12V for
the self parking action, the other two, + and - 12V for the
motor. The self parking 12V is fed from Ign switched, the
12V wiper run from the wiper switch. Switch off the
wipers, the motor runs on the Ign switched, until a gap
on a slip ring, the parking posn, is reached, and the motor
stops in the parked position.
Motors are prone to seize up due to their iron shaft, in
a diecast casting, getting water past the O-ring seal,
resulting in rusting and freezing up solid. The motor,
if you are lucky is still ok, it often is, and you only
need to dismantle, clean and relubricate.
Failure of self parking can be due to a phosphor
bronze contact finger running on a track on
the main gear, losing its spring action, bend slightly,
not too far, or there will be too much pressure, and it will
wear rapidly. Lubricate the track finger runs on. Front
multi-speed wipers may have several PBronze spring
contacts on separate tracks.
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