I love the corner lights on the 1987-1990 Buick Park Avenues, where they only light up with the directional signals and allow you more light going into the turn.
On the 1989 Buick Electra, I took it for granted that the corner lights were functional also. They are not and they have no hole in the back of them to put a bulb.
My project upgrade was to hit the junk yard and get PA corner lights, bulbs, wiring to help these old eye see better at night. After looking at the 1990 PA donor car'* wiring and later wiring diagrams, I couldn't see how to simply tie into the circuit so, I chose a route that was easier and more unique-yea for easy. I removed the wiring, amber bulbs/sockets and foam gaskets from both front lower turn signal light housings (blue-hot/1 black-ground-1 brown) with the intention of making the corner lights into parking lights and to blink with the tiny small side signal. All I needed to finish project was: 4 quick connect splicers, wire trimmer, and needle nose pliers.
The pliers are needed because the signal light bulb socket has a small tab on it to prevent it from being placed into the wrong "port". It'* easy to figure out, just twist the tab off. I used 2 foam gaskets so that the socket would really be secure in the corner light hole, it'* snug but it will go in. Only the 2 wires(blue/dark brown) exiting directly from the bottom of the bulb socket will be used and spliced into the front lower parking wiring which are blue/dark brown as well. The black wire on the side is for the signal light function, which caused my signals to hyper flash, hence not used as a signal light. Turn on the parking lights and then probe the car'* existing wiring for the hot wire which should be blue. Simple, cheap easy project and it subtly adds to the appearance.
The 2 black rotary screw ***** on top of the headlight housing will release the headlights for removal. Carefully separate the chrome molding from the light housing, I gently used a screw driver to get to the corner light screw. Had photos can't load but they are not necessary, it'* that simple for a DIYer.

sounds like a neat little upgrade- as an owner of a 1990 myself - I did not realize there were no cornering lamps on the base Electras - if you can pics would be pretty neat to see

Will try to get photos of install uploaded. In the photo gallery is my Copper Beige 1989 Electra with the Corner light as parking lights.

Where are those pics?

I agree, I wouldn't mind pics either. I would be concerned that it would put an inconsiderate amount of light in the wrong places for other drivers, especially given that they will be on anytime the park lights are on.

At the surface, it seems that running relays off of the power feed between the turn signal switch and the flasher would yield a more considerate result.