Hi, I Have a swollen Lymph node on the right side of my neck. Posterior Triangle I think its called. Can a abcessed tooth cause this?

Possibly. Infected (abscessed) teeth can cause lymph nodes to enlarge. So can gum disease, ear infection, sinus infection, etc. You need to be seen by your Dentist. If your lymph node's enlarged, the infection is spreading.
Yes. If you think you may have a peridontal or apical abscess you should see a dentist ASAP.