I would highly suspect that there is a bulb out. Remove the Eight million hand tightened screws and the trunk lense will come out to access the socket. But check to see which one is out first.
Blown bulb.
This varies with model year.
The trunk
.
yes.under left side of dash
Bulbs or turn signal flasher, maybe even the switch.
Could be a burnt out bulb or a bad flasher unit.
More than likely the Flasher Relay is bad.
replace the combination switch on the turn signal stalk
Because its a 1988 Buick LeSabre
Where is the thermostat located on a 1987 Buick LeSabre?
where is the ecm on a 2000 buick lesabre