Aside from the Fuse/Relay boxes in the engine compartment, there are two inside the passenger compartment. One is on each side of the transmission hump in the front foot area.
mine does not have one
I believe they are located on the starter.
Curb weight, 3,309 lbs
The original wheel size is 15"
Regular ethylene glycol antifreeze............
It uses a distributorless coil pack and a crankshaft trigger sensor.
I just purchased a 1990 Buick Riviera with 45,000 on it for my daughter. However, I did have a brief period that you discribed with the car stalling out. I don't know if this will help, but I just read at another site, that it may have a faulty idle air control.
1990 lincoln town car
If both sides (right and left) don't blink on and off, the blinker "can" may be the culprit.
Kind of bolts- they use both metric, and SAE so you will need a full toolset for both.
inside , right by the drivers right calf, it's hidden behind a pull out panel
fuel filter location in 1990 buck lesabre