Okay, first turn the signal on. The look to see if the lights are blenking If the outside lights work then the little light in the dash is out. If the lights outside don't work you either wire problems or you need to replace the light socket.
Don't forget to check the signal flasher relay.
replace turn signal flasher
Try checking the turn signal flasher. Not to be confused with the hazard flasher.
The signals and the emergency flashers have separate circuits, separate fuses, separate flasher relays. Start with checking the fuses, the bulbs, the signal flasher relay and wiring and if it still doesn't work it may be the signal switch is bad.
Might be turn signal flasher
Check fuses and turn signal flasher
For most vehicles the hazards and signals are two separate circuits, they have separate fuses and separate flashers. Check your signal light fuse and signal light flasher.
The 1998 Lincoln Navigator trailer turn signal fuse will be in the fuse box. The trailer turn signal fuse will be one of the auxiliary fuses at the bottom of the second column.
Could be the bulbs or the fuses or the flashers or the signal switch assembly
Both fuses # 13 and # 18 are 15 amp fuses for the electronic flashers ( it doesn't show which is the hazards and which is for the turn signals )
Probably turn signal flasher is bad
The fuses for turn signals, I assume you are speaking on a Geo Prism, would be located to the left bottom(to the left of your left leg) front drivers side panel.
If the turn signals are not working properly on a 2002 Chevy Venture and the fuses seem to be alright, check for burned out bulbs in the turn signals. Also, check to make sure the turn signal flasher is working properly.