Following info gotten from the Dodge Windshield Wiper Test - from Chrysler Technical Service Bulletin D70-8-5 -
circa 1970 - for Dart, Challenger & Polara.

For passenger cars but some info may be helpful in troubleshooting trucks too. Note warning at end regarding DAMAGE caused by IMPROPER WIRING CONNECTION WHEN TESTING. When testing it's best to make a final connection in each step by touching a wire momentarily rather than snapping on an alligator clip.

1] Disconnect motor leads at motor. Connect jumper from Battery Positive terminal to Wiper Motor terminal 'H'. Motor should run at High speed. Ground is completed through motor frame to chassis ground. Remove jumpers.

2] Connect jumper from Battery Positive terminal to Resistor terminal. Connect second jumper from second Resistor terminal to terminal 'L'. Motor should run at Low speed. Remove jumpers.

3] Connect jumper wire from Battery Positive terminal to Motor terminal 'PL'. Connect a second jumper from Motor terminal 'PL' to terminal 'L'. The motor should Park. If wiper blades are near bottom of glass Motor may already be Parked. If so, run Motor as in Step 2, until blades are high on glass, then repeat Step 3 to observe Parking. Remove jumpers.

To properly test the 2 Speed Wiper Motor on Dart, Challenger or Polara the following procedure must be followed:

1] Disconnect Motor leads at Motor. Connect a jumper between Battery Positive terminal and Motor terminal 'H'. Connect second jumper between Motor terminal 'P2' and Ground. Motor should run at High speed. Remove jumpers.

2] Connect jumper wire between Battery Positive terminal and Resistor terminal. Connect second jumper between other Resistor terminal and terminal 'L'. Connect a 3rd jumper wire between terminal 'P2' and Ground. Motor should run Forward at Low speed. Remove jumpers.

3] Connect jumper wire between Battery Positive terminal and Motor terminal 'P1'. Connect a second jumper wire between Motor terminal 'L' and Ground. Motor should run in Reverse Rotation for at least 1/2 turn and Park.

The following procedure is used to test a Variable Speed or 3 Speed Wiper Motor.

1] Disconnect Motor leads at bulkhead disconnect. Connect jumper wire between Green lead and Ground. Connect a second jumper wire between Battery Positive and Brown & Red wires in bulkhead disconnect. The Ground circuit is completed through chassis ground. The Motor should run continuously. Disconnect jumpers.

2] Connect jumper wire between Green lead and Brown lead. Connect jumper wire between Red lead and ground. Connect a 3rd jumper wire between Battery Positive terminal and Blue lead. Wiper should run to Park position. Disconnect all jumpers.

On a Variable Speed Motor if the unit passes this test then the rest of the Motor Variable Speed Control is accomplished through a Rheostat Coil inside Switch mechanism as knob is rotated. May be possible to disassemble Switch and access Rheostat Coil. In the past on other similar controls/switches I've been able to jumper the broken end of such a coil by soldering a wire of heavy enough gauge, restoring continuity to coil circuit. Rheostat Coil has a flat wiper blade that rides along surface of coil so it may be necessary to file down your solder work for smooth transitions.

CAUTION: MOTOR MAY BE DAMAGED IF NOT WIRED CORRECTLY PER INSTRUCTIONS.

If wire colors or layout doesn't match or look right you're better safe than sorry! I'm searching for further truck specific information, haven't found that TSB as yet. Otherwise use the above info at your own risk because it's NOT specifically for Dodge Trucks. Wiring picture for the motor described shows a square connector with 4 wire connections marked 'H', 'L', 'P1' & 'P2' and with a rectangular white bakelite Resistor with 2 terminals [looks just like an Ignition Ballast Resistor] & attached to motor frame. Another type of Resistor is somehat rounded, encased in dark plastic with 2 wire terminals and is attached to rounded edge at motor frame.