I have a deathCount scoreboard called
Death with a repeating always active command block with the command
/testfor @p[Death=1] on singleplayer. Even when
Death=1, the connected comparator doesn't turn on.
The correct syntax for the target selector argument for scoreboard values is
NAME is the name of the objective and
X is an integer number. The former checks if the score is less than or equal to X, the latter is for greater than or equal to X. For a true equals, you need to put both.
In your case, you'll want to run