Old Man Uses Witchcraft to Avenge Granddaughter's Death

The film I'm thinking about dates back to the 80's. I can't remember much about it, but I found it really creepy and I'd love to see it again.

A man visiting a rural American town accidentally kills a young girl who runs out in front of his car. The girl's grandfather (who the other townsfolk refer to as "OLD MAN DERMOT" or something similar), is very angry with the man and uses black magic to punish him. At some point the man has a seance, and he engages a medium to try to block the curse the old man has put on him. Whilst the medium is in a trance, the old man bursts into the house and kills her by stabbing her to death (without saying a word to anyone if I can recall).

That's all I can remember, but if anyone remembers this can they let me know?

Thanks, Debbie - UK.