Hmmm. This is a tough one. I have only stabs in the dark...
Ghoul minus tool - A gravedigger or graverobber without his tool, e.g., a spade or shovel, would not be able to work--he would no longer be regarded as a wright (from Old English wryhta, worker.)
Thus, a wright, minus his necessary tool for work, loses the 'gh' that made him a wright, and is left with writ (past tense/past participle of write).
right and rite both involve acting in an upright, straight, proper manner, with etymological roots in:
Greek, orektós - upright;
Latin, rēctus - accurate, righteous, correct, straight, virtuous;
Latin, rītus - rite, custom, ceremony, fashion, sacramental, consuetude.
That's all I've got so far. - I have to go, but I'll come back to at least cite my references for the above, and perhaps another idea will percolate up from my subconscious!