I have a 1990 Mercury Cougar. Several problems...Blinkers, hazards, horn, and break lights are not working. However the break light in the back window comes on when the break is pressed. Checked fused and bulbs. Also filled the tank tonight and "CO" displayed for about a mile then went away. Manual simply says there is a problem...take it in. Well I can't really afford to take it in... Any help is appreciated.

I am unaware of what a "CO" display is.
Now with the blinkers, hazard, horn and brake lights not working that may be the multi funtion switch (blinker switch) that is located inside the column (where the blinker lever attaches).
Obviously the blinker, hazard and horn will all work off of something in the column. Brake lights, you may think a switch on the pedal.

the brake lights do work with that switch but when you have the kind of tail lights where a turn signal light shares the same bulb as a brake light, the brake light is cancelled for the turn signal by running through the multi function switch inside the column.
The third brake light does not blink so its not on that same circuit.