Based on your description and location, the bumps could be plugged hair follicles (comedones), infected hair follicles, or less likely (since there are multiple bumps) small skin tumors such as sebaceous adenomas, basal cell tumors, or melanomas. Plugged hair follicles can be secondary to an underlying hormonal disorder such as a low thyroid, or excess steroids; these hormonal conditions are not uncommon in older terriers. You can try using Stridex pads to gently cleanse the areas 2-3 times/week, but if the bumps persist then I would recommend that your dog be examined by your veterinarian for appropriate diagnosis and treatment.
Good luck,
Kimberly Coyner, DVM DACVD
www.dermvetvegas.com
My 5 year old poodle/yorkie has the same exact thing! Some have scabs and others are almost like blackheads. They don't bother her either, but when I pet her a feel them. And when I get her hair cut you can see them. Some of them look like scars, maybe from when I scratched off the scab? They started out by her tail and have spreaded to the back of her neck.