My money is on the relay if you are at all handy and can find the correct relay in the box they can be repaired if you are careful
if you look at the bottom of the relay where the connection legs are you will see if yyou look close that the plastic cover can be uncliped using 2 small screww drivers if you are lucky the relay will have a pair of contacts inside that can be cleaned if not you need to look for signs of burning on the components or circuit board if this is the problem you are probably better off to replace the relay ( lots of cash)
there is one other possibility that being that there is a poor earth connection on the motor
This can be tested by simply running a wire from the motor casing to the negative -- termina on your battery make sur you have a good contact at each end
Good Luck
Roger
April 2008