It's ironic that you ask me this question today-- i am just now carrying in another eMachine computer to fix. Anyway, unfortunately I do not have one that is the same model as yours (T2742). However, I did some quick research and found that yours has the same exact motherboard as the T2898 which I made the diagram for!
The following eMachine models share the same motherboard (and thus the same front panel layout):T2742 T2796 T2798 T2824 T2885 D2823 T2862 T2896 T2898 T2958
For further reference, I would like to share this diagram for the eMachines T6544 in case someone else may need this model. This is the computer I just carried in... might as well share.
By the way, the power switch doesn't need to be oriented any particular way (positive and negative), which is why the switches are not labeled as + or -. Switches can be wired either way and they will work the same.
Hope this helps.