Is your layer shorter than your comp?
Ok but you wanna to loop last part of your logo (with movement) or you wist to stop ypur logo close to the end and leave electric effect moving on it for some time?
If it is the second answer try to read more about time remaping (select your layer on timeline, press right mouse button and chose time/time remaping) and just extend last frame of your logo and of course extend a layer with your electricity effects also.
You can just loop it with an expression. Or, you can split the layer at a certain time, precompose it and loop that certain part. Here's the loop expression that you need to add to the time remap property: loop_out(“cycle”,0)
If you're not sure how to do it, here are the steps below:
Hope this helps.