Thanks for all the replies.  The tractor is a New Holland TG245 so it would be similar to a Case IH 245.  I'm going to redo the wiring and make sure both radio's are supplied with 12 ga wire and separate circuits and see if that helps it. The tractor from the factory didn't even have an external AM/FM radio antenna so I added an external one since the one under the cab roof didn't work very well, but that did not help with the problem.  So it leads me to think all the suggestions about power supply would be more likely---since the stations are lost---like when you disconnect a battery.  Thanks for all the replies