Kenaz analysis
The Old Norse term for boil (generally associated with the equivalent rune in the Younger Futhark) is Kaun (derived from Proto-Germanic *Kaunaz (meaning a sore or boil). *Kenaz (from which we get the derivative mentioned in the OERP) means torch. It is certainly possible that both roots were associated with this rune in the Elder Futhark.. Current convention, however, is to refer to the rune by the root of the rune name in the Old English Futhorc because it is generally assumed that this system represented an expansion of the Elder Futhark and might preserve more of the original structure when compared to the Younger Futhark. Personally I find very little evidence of this assumption's validity, however.
I have generally associated carbuncles/red garnets with this rune because cut en cabochon, they visually resemble a sore, and when facetted, they display particularly well by firelight (in the middle ages, they were thought to contain hidden embers, hence the name carbuncle). However this is somewhat subjective, and should not be taken as traditional.
I think the association between an infected sore or boil and a torch exists because both have a burning appearance and appear to generate warmth or heat. There is also a lightening effect of grief mentioned in the ONRR.
The ONRR is downright pessimistic about this rune. As always you have two images: children dying of sores, and people becoming pale with grief.
The OIRP presents three images of an ulcerous sore: That of children dying of them. The painful spots that they manifest, and the abode of mortification (perhaps the open barrow alluded to above by others in this thread).
The OERP presents the image of torches lighting a hall.
Now, the Younger Futhark has no direct equivalent to Elhaz/Algiz. The lore of this rune seems to have been divided among As (from Anzuz for sovereingty aspects), Kaun (from Kenaz for the effect on children), and Mannaz (battle aspects). So I am inclined to focus instead on this rune as the burning rune and largely disregard the "fatal to children" images (better seen under Elhaz/Algiz). If people ask I will write more in why I make this case. But it distracts too much from this discussion to put it inline.
So instead, I would argue that you have two aspects: The burning aspect-- heat, burns, fire.... And the lightening aspect. These both could be associated with the inspiration/frenzy aspects of Odhr. It could be seen as the fire of the forge. It could be seen as illuminating knowledge provided that the fiery inspiration accompanies it.
This is (in my opinion) what is seen in the 4th part of Havamal (the Runattals Thatr Odhinns) where (as I paraphrase):
Word followed word,
I found words
Work (or song? or incantation?) followed work,
I made works.
(this is where the 9 incantations he learns doubles to 18).