Need a tail light for 1991 Bonneville Pontiac

http://www.bbbind.com/free_tsb.html

If the right side works it's not your flasher, Its your left side bulb, either front turn signal or rear tail light bulb.

There are butterfly nuts inside the trunk right behind the taillights and the carpeting take those off and the taillight should fall right off and turn the light plugs counter-clock wise half turn and the light bulbs will come off

has the fan belt or drive belt for the power steering broke by any chance

No park lights on right side, front or back?
Use a testlight and see if power is present at the contacts in the socket with park lights on. There may also be a separate ground for right rear, but I doubt it. If you don't have power to the socket, look for a broken wire between the left rear and right rear. (The socket will have two contact points-one for park lights, one for brake and turn signals.)

1987-88 Pontiac Bonneville Stereo Wiring Constant 12V+ Orange Switched 12V+ Yellow Ground Black Illumination Gray Dimmer Brown Antenna Trigger Pink Antenna Right Front Front Speakers 4" x 6" Dash Left Front (+) Tan Left Front (-) Gray Right Front (+) Light Green Right Front (-) Dark Green Rear Speakers 6" x 9" Rear Deck Left Rear (+) Brown Left Rear (-) Yellow Right Rear (+) Dark Blue Right Rear (-) Light Blue

to remove open trunk remove covering behind light.remove plastic retainers from behind lamp. pull light out remove sockets,

you need a head light switch. buy from carquest (significantly less expensive then dealership).
remove knobs (small insert on pull knob press in with a small flathead while pulling towards you, twilight knob pops right off)

take off the cover plate over steering wheel (pop out with flat head screwdriver)

then cover over instruments (small torx bit 5 screws, 2 hidden by previously removed cover).

three small bolts hold in light switch.

http://www.compnine.com/largeimg/9410173C10-017.gif

may help in clarification

The whole lamp comes out and the bulb is change from the back side.

Unfortunately There are only 2 Places to Purchase these Lenses. A Salvage yard or the Dealership.