You should not have any power to the motor when the relay is off, so its odd the LED is lighting up. Add a second smaller relay, that is energized when the main fan relay is energized, that should isolate the LED from any leakage voltage that may be keeping it on.
You should be able to tap right off the positive wire at the relay for the fan, just be sure you are on the output side and not the input, post #87 should be the switched on/off post, #30 is the battery feed, the other two are the switching wire from temp sender and ground.
