What is the clear yellow liquid draining out of my arm infection?

Normal drainage. If you have an arm wound that is open, it is normal to have some clear, yellow drainage from it. If it were infected, the drainage would look like pus, and you would have a reddish color in the area and increased discomfort. It should disappear as wound heals and closes.
Serum. Often the clear yellow fluid is from edema and normal body fluid leaking around the site of infection. It may contain white blood cells that were sent to help fight off the infection.