Diagnostic tools?

Anyone have any experience with either of these (or anything similar)?

<a href=http://www.eastwoodco.com/shopping/product/detailmain.jsp?itemID=1378&itemType=PRODUCT&iMainCat=627&iSubCat=628&iProductID=1378>Short Circuit Tester</a>

<a href=http://www.eastwoodco.com/shopping/product/detailmain.jsp?itemID=1411&itemType=PRODUCT&iMainCat=627&iSubCat=628&iProductID=1411>Fault Finder</a>

It seems like these could come in quite useful with our old cars. I've got an occasional short circuit somewhere in the brake light circuit that blows the fuse slowly. You can actually watch the center of the fuse change color and slowly melt away (after about 5 seconds). There must be a short somewhere that has high resistance.