The blinker stopped working on my 92 dodge dakota. I replaced the wiring on the rear lights and the fuses are good. The taillights come on when the brake is pressed, and the lights work at all four corners when I manually shift the turn signal up and down. I am stumped.

First check all your fuses.
https://www.google.com/search?q=cig+lighter+fuse+panel+on+92+gmc+half+ton&biw=1361&bih=650&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj_--aUpbvQAhUE4yYKHTvTBg4QsAQIKw#tbm=isch&q=1992+GMC+C1500+fuse+panel+location

If all fuses are good, you may have a wiring problem. If you are mechanically inclined, will need to remove the required components to expose wiring and see if you have a break somewhere. Most wiring harnesses run along inside of vehicle trunk. Then, they continue under rear seats and possibly under carpeting.

Did you check for voltage at the 50 amp fuse circuit. Even if the fuse is good if no voltage on the fuse circuit, the circuit is still dead. There is a light green wire that carries voltage from headlamp switch to dimmer, is that wire hot with headlamp switch on?

There are wiring diagrams for free, just about everywhere, if you don't have one. Autozone .com has free wiring diagrams on vehicle repair guides link. You have to register your vehicle, year--make--model, all that good stuff. It's free.

Follow the flasher wiring to fuse box and locate the fusible link. Looks just like the wire but softer exterior and it's a fuse able wire that can break down. Should be along the driver fender under hood.

You need and electrical mechanic. There must be a broken wire or bad connection. You have to check everywhere under and in the back of your taillights. Good Luck!

did you check ALL fuses inside cag and under hood?

Hello.
This sounds like you have a bad ground on your Dakota. Trace the wires back until you see that one of the wires is connected to the body or frame with a small screw or small bolt. Make sure that your have a good clean ground to work with.
Another thing that you can check for is to see if there is another light out somewhere else on the truck. Its like christmas lights, when one bulb goes, it can effect all the others just as well. The only other option is to check your fuses, get the fuse diagram and see what controls the taillights. On my truck I have the wrong fuse in there cause only the taillights to work and not the brake lights. Vehicles are very picky with there fuses. If the correct fuse is in there, make sure that the fuse isnt burnt out. You can check that by seeing if the filament in there looks burn or is broken like it popped. Hope this helps!
-Steve

check the fuse, it is usually located under the dashboard or between the door and the dashboard.

www.wiring-diagram.com
You can get any wiring diagram for any vehicle. It will cost about $12 and it's well worth it. It will give you the complete diagram bumper to bumper.

Check the fuse panel info in your owner manual. Check out the fuse but it will more likely be a corrosion problem where the ground wire leaves the tail lights and bolts to the frame. To uncorrode your ground wire purchase a spray can of electrical wire cleaner at the autoparts store.

please mark this answer as a fixya! ty.

you have a bulb out or your relay is shot