My brake light is on in my 91 dodge dakota

Replace the whole cable.It would stretch in front & the rear the same amounts.

first check that the cable to either side moves freely when you pull the cable down. You will hear the brake shoes move in the drum. Next where the cable goes through a angled section from one wheel to the other and where the lever cable attaches to this point there will be an adjustable bolt for the lever cable . adjust this nut until there is about 3-4 clicks on the hand brake lever ratchet. When finished jack up one side and ensure that the wheel spins freely with the hand brake in the off position.

where the cables connect to the rear parking brake shoes is like a hook shape waht iv seen happen is thay rust and stick after being aplied only real fix is to remove and free them up and re assemble the parking brake taking the cables off wont release the shoes from teh drum and will cause more damage in more parts will be needed to compleat the repair

Replace the rear rusted parking cables

Not sure but the last post on this link has some solutions which should not cost anything

https://dodgeforum.com/forum/2nd-gen-dakota/229748-abs-light-and-parking-brake-light-on.html

This is a big job for such a small part. I suggest you repair/replace rotors, pads, and anything else back there while you are at it. You will need to remove both wheels on both sides, as well as the axles (I think). See my earlier post on Rear Rotor removal to see how this is done.

You will need a large spindle nut to remove the axles.

DISASSEMBLY:
Once you have access to the parking brakes inside the rotor hat:
1. Lock out the parking brake w/a pair of Vise grips (on the parking brake cable under the cab)
2. Disengage teh park brake cable from behind the rotor assembly to allow easier disassembly of the parking brake shoes.
3. Disassemble the rear park brake shoes.

REASSEMBLY:
1. Reassemble the rear parking brake shoes. This is a typical, small brake drum configuration. Do one side at a time - so you can see how to reassemble each small part. Keep the springs and parts oriented the same: front to front and interior to interior, etc.
2. Release the parking brake cable
3. Install the disc brake rotor(s)
4. Install the disc brake caliper(s)
5. Install tire & wheel assembly
6. Lower the vehicle

you mean parking brake cable? loosen parking brake cables put drums on , and adjust shoes till they lightly drag, now apply brakes a few times and check the adjustment again, if all ok, now adjust park brake cables, you want to adjust so park pedal goes 5-8 clicks till the wheels are "locked up" and the wheels spin free with the park brake off

check fuse first, or it's a ground problem somewhere try new ground wire at interor light and on at brake light , regound them right at the problems to steel

when brake light is constantly on it normally means the rear brake light dont work (bulb blown) ABS normally means sensors pushed too far or teeth on abs cv axle could be damaged or bent. check that first.

What happens when you run a jumper wire from another fuse cavity, directly to brake switch?