Why won't the turn signals(blinkers) on my car's dashboard work?

I own a 1985 Ford F150 XL and I'm currently sixteen fixing up the many problems the car has due to it's age and how many salt water floods it has been in down at Eureka, California. For some strange reason when I started my car, I tested my turn signals when I noticed that when I put on the right or left blinker the lights on the outside of the car work. Now when I turn them on from the drivers seat, the indicators on the dashboard do not turn on at all. So now I can't tell which turn signal is on when I'm driving. I better fix them because it can be dangerous. Anyone please help.

Replace the bad fuse for the instrument panel.