Question about I2C cable

[Dewster]

Hello, 

I picked up a Netserver LC 3 today (heavy little buggers) and am gathering a parts list to get it running again. On the motherboard, I noticed two "I2C" ports. One is yellow and the other is red. It already had a cable plugged into the yellow port which then plugs into one of the two yellow ports on the hard drive caddy. There isn't anything plugged into the red port on the motherboard. My question is, what is the red port for and do I need a cable for it that plugs into the second port on the hard drive caddy?

Thanks!