hi rpm overheating
 

I have a motor question I have twin Mercruiser inline 4 cyclinder 3.7 LX
motors one has run fine the other
however seem to begin to overheat when rpm get over 3000. these are
freshwater cooled. while trying to figure this
out we noticed that in the over heating motor down on the bottom when we
squeeze the hoses to see if we have water moving
we dont get and movement in that area its a little box with some wires
coming out of it Ive been told maybe its a voltage regulator?
cant really make heads or tails from the repair manual. I know this isnt
much to go on but could but it seems to be the one area
where we have a difference. does anyone have an idea of what Im talking
about or what I may be able to do to repair this issue

Thanks

Paul