electrical and lights on 1994 Mercury Villager

1. My left brake light won't come on. Tail light works fine.

2. My speedometer (digital) is sporadic. More off than on.

2 answers
If your speedo drops off to 0mph while driving then your speedo sensor is bad. Easy to replace.
Have you change the bulb as its a dual element bulb so the brake light portion can go out and the tail lights will still operate