Reading Tablature

[Bamakathy 0]

When looking at tablature, is the top line or bottom line the heavy string on the dulcimer?

[NoterMan 14]

Almost always the top line of tab is the bass string and the bottom line in the melody string.  The Tab should tell you which is what; however many careless people write 1-5-8 tabs as DAD instead of DAd, which is more proper. 

One of many reasons why tunings should be referred to by their 'relationship numbers'.  1 is always the bass string.  Middle string is almost always a 5th above the bass string, and the melody is between 2 and 8 above the bass string.  ALL 1-5-8 tunings use the same tab -- DAd, CGc, AEa, GDg, etc.  All 1-5-5 tunings use the same tab as well DAA, CGG, EBB, etc.