Hello Jay
I would first check your voltage regulator Three wire connection to make sure that it is a good solid connection. It will be on the same side of the engine as your Oil filter is bolted down into the upper area of the engine blower housing. In keeping in mind the charging system is not up to par in your tractor it may be due to the rear of the fly wheel might be packed with old Oil and dirt debris. My 1983 318 was not charging well unless it was in Three quarter's to wide open throttle position like your's is doing. I took mine apart a couple of year's ago to replace it's engine and the rear of the fly wheel was Packed solid with old oil and dirt. I had to use a screw driver to dig all of the crusted over oil and dirt out of that area, The stator was buried in old oil and dirt and I could not believe that it charged at all due to this massive build up in and around it. It may be the reason of why your stator is not putting out a good charging Rate unless it is in wide open throttle position. The bad part is, the engine must come out to see if that is the problem. being that the stator Pick's up it's charing from a Magnetic field the build up may be hindering the correct Operation of it. Mine is now charging as it should the light goes out through the entire RPM range and my battery stay's charged up fine. I hope this helps, Kurt
