Very good advice from Rich. I'll second his mention of the poor quality H4 plugs. I got my H4 female plugs from Daniel Stern Lighting.
http://www.danielsternlighting.com/products/products.html
Their site doesn't list the part number, but he sells a very nice high heat female plug end that has spring-loaded wire connection terminals. Pretty trick little plug end. I think it's made by Hella, so quality is good.