I have a 12v DC linear actuator, it just has 2 wires coming from the motor.
If I connect the red wire to the positive terminal of the battery and the
black to the negative, the motor extends. When I reverse the wires the
motor retracts. The motor draws about 5 amps. Pretty straight forward even
for an electrical dummy like me :)

I have a grip for my control stick that has a 3 position switch to control
this motor. It is an ON-OFF-ON SPST switch that is capable of about 2 amps.
So I went down to Radio Shack and bought a DPDT 12v relay part number
275-218. Here is the Radio Shack web site for this relay:
http://www.radioshack.com/searchsku.asp?find=275-218

I need some help wiring the thing up so I can use my motor. Which wires go
where? Did I get the right kind of relay?

Thanks,
Jeff