Most likely bad turn signal flasher or could be a problem in steering column
Ensure relays and parking brake switch are properly functioning.
Probable causeFlasherFusecontrol lever
one of the lights is not working
Yep, one for the signals and one for the emergency flashers.
You have a short in the wiring or at one of the bulb assemblies.
Aren't they different flasher relays
Check the turn signal relay. The four way flasher and the turn signals each have their own relay. It has a fuse for the turn signal
Multifunction switch is bad.
Maybe not aligned properly may have to install shims
There is no timing to set. The timing is controlled by the ECM with signals it receives from various sensors.
The voltage gauge on the Blazer is not the most accurate (cheap) When using the signals the voltage draw on the system is enough to make the gauge move slightly.
If installed properly and maintained, it will not be harmful.