If I understand correctly, you have Sylvania 170 timer and the display doesn't light up.
If you have different problem, add a comment.
A) If this is existing installation
and timer display worked correctly before, then it sounds like timer malfunctioned or power to timer is interrupted. Check breaker, and then pull out timer and test for power.
B) If this is new installation
, then 2 possible things:
1) Timer defective: exchange for new one.
2) Timer not wired correctly.Review wiring
Timer replaces single pole switch.
Single pole switch has two wires
Timer has 3 wires: Blue Black White
Timer has additional wire to run internal clock and to light up display.
If timer not wired correctly, then display will not light up.
Here is correct wiring:
a) Two wires from switch.
b) Connect timer-blue wire to one of the switch wires. Choose either one for now. You will have to choose other wire if display doesn't light up.
c) Connect timer-black wire to other switch wire.
d) Timer-white wire does NOT connect to either switch wire. Look in back of electric box. There are white wires twisted together and covered with wire nut. These are neutral wires. Connect timer-white wire to neutral wires. This will power the clock and display.
e) If your box does not have the white wires described in d), then connect timer-white wire to bare ground wire.
f) Turn power ON. Does display light up?
g) If display lights up, switch is wired correctly.
h) If display does not light up, then reverse timer-blue wire and timer-black wire shown in step b) and c).