Well, I spent some time screwing around with the circuit board relay without much luck. So, for the interim (and maybe long term) I installed an Inpower timed relay connected to the carb fan and thermosensor. I'm able to adjust the timing between 0-60 minutes and it comes on when the exhaust manifold temp hits 185 and I turn off the ignition. Then turns off at a predetermined time setting. It's actually a pretty slick little mod I learned here on Mud.