I have a remote control car and its remote that I gutted and wanted to control the remote by opening and closing the four switches (up, down, left, right) with the arduino over the ethernet shield.
I've managed to get the remote open and soldered two wires to the "forward" control so I can use it with a breadboard. I've verified that by touching the two wires together, the signal is sent to the car, a small LED in the remote turns on and the car moves forward. The voltage across these two wires is 2V according to my multimeter.
I'm just unsure how to use the arduino to close this circuit and hence move the car forward. I'm entirely comfortable with using it to control LEDs and Servos, etc. over the ethernet, that's no problem, but don't know what electronic circuit I have to make to close the circuit. I've got a bunch of 2N3904/2N3906 transistors which I was told would be helpful and were given to me, but unsure where to go from here.
Use a multimeter on continuity mode, one probe on the first wire you soldered to the board and the other probe on a ground point and see if the meter beeps. If not do that again for the other wire. Also maybe look on the pcb and see if you can work out where the copper tracks go.
Maybe you should have a look on google to see how switches can be used in circuits. You will probably find that one end of the switch is common to the rest of the switches.
Basically you should only need to solder one wire to the switch position for the Arduino not two.
I had checked by connecting each of the wires to the ground pin of the arduino and nothing happened each time. I'll check on the multimeter when I get home.