Two quite distinct-looking Welsh texts (both attributed to William Williams) are given in different sources as the Welsh original of the hymn "Guide me, O thou great Jehovah" (English by Peter Williams). One starts with the stanza

Arglwydd, arwain trwy'r anialwch,
Fi bererin gwael ei wedd,
Nad oes ynof nerth na bywyd
Fel yn gorwedd yn y bedd:
Hollalluog, Hollalluog
|: Ydyw'r Un a'm cwyd i'r lan. :|

while the other is

Wele'n sefyll rhwng y myrtwydd
Wrthddrych teilwng o fy mryd;
Er o'r braidd 'rwy'n Ei adnabod
Ef uwchlaw gwrthrychau'r byd:
Henffych fore!
Caf ei weled fel y mae.

Can any Mudcatters help me figure out what really is the text underlying the English hymn text, and what if anything is the English for the other?

Liland
who suddenly wishes he knew more Welsh