1990 toyoto pickup truck. signal lights do not work.

You have one flasher for your turn signals and one for your emergency flashers. If one turn signal works then it isn't your flasher. I would look at the connector under the bed where the trailer plug splits off. This is a common place for corrosion. With a 12v test light you can probe from the light for power. If there isn't anything at the connector at the light move up to the splitter. If you have a signal there your problem is between it and the tail light.

It could be a loose wire or a dodgy (lol) flasher unit

Check the switch and may be on seperate flasher unit

pickup a test light and check all the fuse if the fuses are good then you probably have a bad signal flasher.make sure you change the signal flasher and not the emergency flasher as they look the same.

may be in signal selector switch....

the turn signal flasher is a small canister-shaped or rectangular unit located under the dash, either in a clip adjacent to the steering column or in the convenience center which is located located under the right side of the dashboard and houses relays and other components. The fuse.faulty flasher unit a broken switch or a loose or open wire. We have eliminated the switch, I would check all fuses inside and out, you can replace the flasher with the hazard flasher as if I remember correctly they are the same shape and size, then it is just a matter with a tester light running it from the column to the sockets and finding the break. Hope this helps Tim

check all bulbs,inspect sockets for corrosion,rust ,or sighns of overload.follow wires and check connectors if all good ,replace the flasher ,,if that doesnt fix it ,the blinker switch in the steering coulmn would be next

If fuses are good, I would check the flasher. Located under driverside dash by the steering column.

I think that your flasher is bad I believe that the 4-ways flasher is a seperate flasher unit it should be in the fuse box and look like the 4-way flasher , to find the flasher turn on the 4-ways and you can feel it or hear it flashing and lok for the flasher for the turn signals
Mike

check the brake switch, you might need a wiring diagram to see exactly how the wiring is, but that is a possibility or it could aslo be the flasher