If you mean where is the button to activate the flashers, it is located on the top of the steering column.
If you mean, where is the flasher relay, it is located under the dash. Get on your back down near the peddles and look up under the dash to your left. It is a square black box looking thing.
If you need a flasher relay they are very hard to find from anyone but Ford.
Here is some information.
For Ford part number E80Y13350A
The identical Motorcraft part number is SF-585.
I found a web site that has this for $17.87.
It's a special order for them, ship in 10-15 days.
Here's the link
http://www.carparts.com/index.asp
Not a bad price, compared to $48.82 from Ford even if you have to wait.
I got one for my '90, and it is the correct one.