reverse voltage for boat

When I did the cut and paste when I copied your diagram, forgot to change the name of the third relay from Relay 2 to Relay 3; the bottom relay is the 12V power relay (Relay 3).

The two top relays are the polarity configuration relays (Relay 1 and Relay 2).

The top of the motor is the (+) and the bottom connection is (-), and in the original setup were connected to Input (+) and Input (-) respectively.  

With the use of relays, the two control wires don't need to be heavy gauge or anything, since they're just driving the relay coils, but if they're already run, there's no need to change them.

The 12V power shown should be fused as in HWW's diagram; I didn't draw that in-

Thick lines need to be heavy gauge since they carry power for the motor-

I can not understand how the actuator will go up then stop and then down and stop in your diagram.

What if there are no limit switches?

are there 5 terminals or 3 on the swtich currently being used?

all that needs to be done is wire up the thing like an actuator in a door of a car

Actuators / Reverse Polarity

This is practically identical to the 5 wire alternating 12V(+) system above. The only difference is there's no switch! Both motor legs rest at ground at the relays. To lock or unlock the vehicle, polarity is changed on one motor leg.

We have no Remote and only 2 wires in the dash for switching a low current load.

It is a boat so there is no common ground.