I would start chasing the wiper wires, locate the circuit drawing in the SVM and start digging. Look for any kinks, hard bends, rubbing, crush points and bundles of electrical tape. Will start digging in the manual if i get a chance.
Start checking the wires to the wiper motor and see if any of them are grounded to the chassis, also locate the ground for the motor that should be in the trunk according to the schematic.
Pick one issue/circuit and chase it to the end or you wont make any progress. Also make sure to reseat all connectors and give the wires a slight push towards the pins, intermittent connections can be such a pain.