try Horizon Hobbies completion guides
[link=http://www.horizonhobby.com/Products/RelatedParts.aspx?ProdID=HAN4000&Category=Completion+Guides&SubCategory=Electric+Conversion+Setup]Electric conversion[/link]
-OR-
http://www.horizonhobby.com/Products...ProdId=HAN4000
if these links don't work for you, go to
http://www.horizonhobby.com and try a search for Piper J-3 Cub 40 ARF
When you get that, you'll see and click on:
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Completion Guides