Since a light node makes transactions from a connected full node, does a light node need ethers to make transactions or it uses the ethers from the full node?
The account that signs the transaction is the one that pays for gas. It doesn't matter how the transaction then gets broadcast to the network (e.g. what node it's transmitted from).
So no, light nodes don't need to have ether, and nor do full nodes. (Nodes don't have ether. Accounts do.)