The windshield wipers on a vehicle are powered by a switch that connects or disconnects the power to the windshield wiper motor. When the motor wears out and needs to be replaced, connecting the windshield wiper motor wiring to the switch can be confusing. Unlike other accessories in the vehicle, the motor runs its ground wire through the switch, rather than grounding directly to the frame of the car. Once the motor is mounted on the firewall and connected to the wiper arms, it is easy to wire the motor into the vehicle's electrical harness.
Open the driver side door and use a flashlight to look up under the dash, behind where the wiper switch is located on the dash, to find the wiper switch terminal block. The terminal block will have wires coming from one side that lead back to the switch and the vehicle fuse box, as well as five blade connectors on the opposite side that have no wires connected to them.
Mark the corner edge on the blade connector side of the terminal that is directly across from the white or red wire entering on the opposite side with a white marker. The white ink will be easy to see beneath the dash. The white or red wire is the power wire from the vehicle fuse box. The first blade connector at the edge you marked is the high-speed wiper switch connection.
Cut two pieces of wire four inches long, and strip 1/4-inch of insulation from both ends of each wire using the electrician's pliers.
Crimp a single spade connector on each end of one of the wires using the electrician's pliers.
Crimp a piggyback spade connector onto one end of the remaining wire, and a single spade connector on the other end using the electrician's pliers. A piggyback connector is sometimes referred to as a blade splice terminal, and has a spade connector on one end and two blade connectors on the other end, which allows for two spade connections to be made from one blade connection.
Push the single spade terminal of the short wire with the single and piggyback ends onto the fifth, or last blade on the other end along the connector side. Push the piggyback spade onto the middle, or third blade.
Push one of the single spade terminals of the remaining short wire onto the blade connector on the piggyback. Push the spade terminal on the other end onto the first blade.
Pull the two wires coming from the wiper motor through the nearest opening in the firewall. Do this by following other wires in the engine compartment to where they pass through the firewall, or look for temporary plugs that have been placed in unused holes in the wall.
Strip 1/4-inch of insulation from both ends of the two wires coming from the windshield wiper motor. Most manufacturers have already cut the insulation 1/4-inch from the end, but left it in place to protect the core during shipping. Pull the insulation tips off by hand, or use electrician's pliers to strip it off.
Crimp a single spade connector onto the end of each of the wiper motor wires. Connect the black wire from the motor to the fourth blade on the wiper switch terminal, which is the ground wire connection.
Connect the white, red or green wire from the wiper motor to the second blade on the wiper switch terminal. This is the power wire connection. Tuck the wiper switch terminal back up into the wiring harness of the dash so it is not hanging down.
If the hole in the firewall has no rubber grommet liner, wrap the two wires from the wiper motor with several layers of electrical tape at the point where they pass through the hole to protect their insulation covering from rubbing against the metal edges. If the bare wires become exposed, it cause a short circuit in the electrical system.