I have a 91 geo tracker the brake light comes on and the brakes are hard to push. it also feels like it is pulling to one side

what does pulling mean?
in 2wd and 4wd the rear axle pulls (that i moves the car)
or do you mean the rear brakes drag? (lift car and feel them?)
or while braking the rear brakes, pull.
we cant guess the word pull and its implications, unless you say.

tell what your are doing, when it's pulling?
and what you felt or saw or?

vacuum leak on the brake booster.

Check and top off the brake fluid level in the master cylinder. You should only add brake fluid from a sealed container and brake fluid will absorb moisture an humidity.

Rough idle can be due to poor quality / contaminated fuel to needing a tune up or more.

lose the fittings at the master cylinder, you should have two of them , one for the front brakes and one for the rear, get a friend to push the brake pedal ( not too hard, be careful they may spay all over) ; and see if any fluid is coming out with his pedal down tight the fittings back with the pedal down,so you don't get any air in the lines. If nothing comes out you have a bad master cylinder.

Remove 2 phillip head screws at bottom of taillight.Gently pull outwards on each bottom corner as light comes out drop downward so tabs at top of light can clear . Now you can access light bulbs.Install in reverse order

there is a clear unit on the master cylinder with a level mark. and also chech the e brake lever in the tracker

brake light switch under brake pedal

change the hose

sounds like you have a brake claiper piston not return causing the brake pads to drag, jack up both wheels and spin to see if you can feel or hear drag, give the wheel a hard spin and see if it stops right away or seems to spin freely, could be the drag of the pads on the rotor, or wheel bearings need repack or even as much as brake residual fluid pressure on calipers cuased by improper brake mc pushrod adjustment, if you have had any recent brake work like a MC replacement it could be that it was not properly adjusted as far as pedal free play... check those.. please let me know if this helps, rate my help...thanks

THERE IS A SWITCH UNDERNEATH THE STEERING COLUMN THAT WILL CORRECT THIS PROBLEM. I BOUGHT MY 1994 GEO TRACKER 4X4 BRAND NEW. IT TOOK ME SEVERAL SERVICE APPOINTMENTS FROM MY DEALER BEFORE I GOT THIS INFORMATION FROM MY MECHANIC.