Tridon EP34 or equivalent will work OK. This is a 3-terminal flasher, you connect the green ground wire that hangs loose near the OEM flasher, as well as the power and load wires.
This is a "load sensing" flasher that will flash fast with LEDs, the fast flash is to alert you to a burnt out lamp with standard tungsten ones. I like the fast flash, maybe you won't.
These are available at pretty much any auto store. There are many others. Apparently a 97 Ford Cougar uses one that will work, if they can only look up year/model.
If the fast flash bugs you then special "LED flashers" are available from many online sources but rarely seen in retail stores. They will cost a lot more than auto store ones... although identical except for the load sensing stuff, they're "special" and thus worth lots more, apparently. You can also open the cheaper flasher and change a resistor to make them flash normally (slower) with LEDs. Instructions exist online.
I would avoid 2-terminal electronic flashers that connect only to the two wires for your old flasher. They have to start "off", as the voltage across them charges a wee capacitor that runs the electronics. With the low current through LEDs that can take a while, so you switch on the turn signal and nothing happens for a second or two. The three terminal ones with a ground wire power the electronics directly from the incoming power, and generally start "on": the signals come on instantly when you switch them on, then start flashing. I personally want the signals to light up as soon as I switch them on, in traffic a second or two before others find out I want to turn or change lanes could save a life (mine).
