There is no system, these are NOT electric. They automatically adjust based on the downward force as the bow comes up. What you see is all there is to these tabs minus a few screws.
***SOLD***
Nautilus brand smart trim tabs. These are not electric. Size is 12"x9" and they are designed for boats 17' to 22'
More info can be found at:
www.nauticusinc.com/smart_tabs.htm
$90 shipped