Step 1: Prepare the Tools and the Materials.
Multimeter - for examining the car's wiper control circuit.
Soldering Iron - for building the delay circuit.
Resistors (all are 1/4W) - 100K, 4K, 10K, 3.3K
1 variable resistor, 250K
1 electrolytic capacitor, 24V, 100uF
1 2N4403 transistor
1 2N4401 transistor
1 1N4002 diode
1 5A Relay, SPDT type
Step 2: Build the Delay Circuit
Note that I did not use a PCB in order to make the construction compact.
Use a masking tape to fix the other components on the sides of the relay then solder.
Step 3: Label the Wires and Cover the Construction.
After attaching the label, cover the construction by tape so to make it insulated.
Step 4: Find the Wires to Be Connected in Your Car.
Find the wires to be cut and connected to the delay circuit. The attached schematic in this step is your guide.
Hint: By turning on/off the wiper switch, monitor the voltages in the connector to find the right wire.
Step 5: Last Step: Connect the Delay Circuit
Note: You can replace the variable resistor of the delay circuit into a volume control knob in order to adjust the delay while driving. In my case, I just leaved it fix first until I have time to plan where to put the variable resistor in the car.