my buddy has a 1990 Taurus the signal lights do nt work, he tried replacing the flasher, but it made no difference, if the brake lights are on then you can get one side of the car to have those signal lights shut off, example, you are stopping, you pulse the signal lever to the left, and it will flash (each time you press it to the left that light turns off each time you release it turns back on again) but ONLY with the brake lights on, beyond the flasher he has no idea as to what the problem is, he dosent have a 4 way flasher, but he never had that (correct me if I'm wron the signal flasher is under the dash and the 4 way is in the fuse panel) thanks any help is appricated

Look closely at the turn signal switch. this can cause the problem you describe. Also look for a good ground at the rear of vehicle coming from the lighting wiring.