buring up starter relay

[BOAT DOCTOR]

I have a 2000 suzuki Dt225.After two trips and about two dozen turns of the key starter relay is burnt out.Change the relay three times and every time same thing two trips and two dozen turns later relay stops working.I change key switch,tighten all grounds on motor and at the battery.notice that the yellow wire with green stripe on relay when the motor spins over only has 9.36 volts not sure what it should be but far from 12 volts could this be the problem should it be 12 volts on the yellow with green stripe on the starter relay hen motor is spinning over.any ideas. THANKS