i agree with joey g, switch the 2 relays you have and see if it will go down but not up, and you will have the answer.
if thats it then do as hotrod said and take it to an auto parts store for a 10dollar fix over a 50dollar fix at the marine store.
if its not a relay, check all connections, being loose and corrosion will do ya in, if thats not it,, can also try a test light, have a buddy hit the switch and see if youre getting juice to the relay, if not, see if juice going to switch, and so on,,,