1991 Mercury Marquis wont start sometimes

Electrical problem
1991 Mercury Marquis V12 Two Wheel Drive Automatic? Miles

sometimes when I try to start the car I get nothing even the dash lights dont do anything. Then if I try again it might start. I checked my battery it was 11.86 even after trying to start it unsuccessfully. My battery is only a year old my starter is only 4 months old. This might be a coincidence but I tapped on the positive cable post with a wrench and it started. I also disconnected the coil wire and re-connected it and it started. Ive had the car 4 years ive never replaced coils or starter modules. Also last night when it started and I drove it home from work it lacked power even though it was 50 degrees out.