I have an 89 Dodge Power ram that drains battery while sitting in the yard What can cause this?

A drain somewhere, such as a light that's always on or an accessory that is drawing off the auxillary power

I have the same problem with an 84 D100. I found the easiest solution was to put a battery cut off switch on the battery. I disconnect it with the switch when I won't use it for more than a couple of days. I bought mine at pep boys for under $20, took only a couple of minutes to put on. Really made that problem a non issue. Only downside is it won't save my radio stations.