need help with swc

Hello,
I need idea how to do in easy way swc for car audio radio.
I have 1 wire from car radio "KEY". Example to switch song i need short "KEY" to "GND" with certain resistor.
How i can do this by sending signal from arduino? I have 5 different resistors.

Thanks.

What is the voltage between the KEY wire and Ground?

johnwasser:
What is the voltage between the KEY wire and Ground?

12

Use an NPN transistor between the resistor (Collector) and ground (Emitter). A 220-ohm resistor between the Arduino pin and the Base of the transistor should let you turn the current ON (HIGH) and OFF (LOW). There will be some resistance in the transistor so y9ou may need to adjust the resistors a bit downward.