If you're going to use an electromechanical relay and it is going to be installed in the engine compartment, it needs to be spark protected (like the solenoid on a marine starter motor). Using a relay that is used for something like a trim pump will be good. I decided to use a solid state relay for my electric fuel pump and picked it up from a NAPA store for $18. It's a NAPA "Echlin" AR168 30 amp relay. I haven't looked at the schematic for the criss-cross you need to do to reverse the polarity to the hatch motor for up and down, but the wiring to a solid state relay connects the positive 12 v from the control switch to terminal 85 & the ground to terminal 86. The 12 v positive from the battery connects to terminal 30, and terminal 87 goes to the hatch motor and then from the hatch motor to ground.

easy, use a trim or slave merc relay either will work......

The older OMC' & Mercs used the Ford type for the assist, it will hold more AMP's the the new style and is fully spark protected. I have a few in my stash!