Replace wiper switch on mercury sable

SOURCE: heater doesn't work

This happens ALL THE TIME!! Heater core is likely plugged with rust, yes. but a garden hose fix will NOT last. and the reserve probably IS cracked on bottom, as most are.They are relatively cheap from Ford, though. Have a REPUTABLE radiator shop do a Genuine Power Flush to the entire cooling system (not an automated fluid exchange many shops claim to be a "flush") and THEN have them unplug the heater in a similar fasion. Now is the time to replace the surge tank (old one is packed with rusty sediment that is usually partially plugging the cracks in it, and not very cost effective to clean anyway). On older, very rusty 2 valve 3.0 systems only other issues are the rear of timing cover gasket often leaks a little, and the water pump impellers can become eroded away (from rust) and water flow suffers. So... watch for residue or dripping from behind water pump. If minimal, a mild leak sealant added to a properly cleaned system with refill and tightening the bolts near leak will do the trick--otherwise timing cover gasket and pump replacement is needed.

SOURCE: Windshield wipers don't work

Ok, this is a steering column issue. The wiring needs to be replaced. Shouldn't cost much at all. also, the external switch may have issues as well but, i suggest you re wire your steering column to fix this problem.

SOURCE: I have a 1993 Mercury Sable 3.8 and have flushed

do you here and movement in dash when you switch it to heat it might be a bad switch i have replaced quite of few of them

SOURCE: Heater will not blow heat, heater core needed

If the heater core is not leaking then the core is not bad. It would be filling the floorboard on the passenger side with antifreeze. If the only problem is that no heat is coming out then I would turn my attention to the temp control door. It is controlled ether by a cable or a vacuum pod. It sounds like the control for this door has failed. Try to guide them in that direction. Hope this helps. Good luck.

SOURCE: 98 sable -no heat. changed thermostat, new

Since your blower is working and it is a heat issue,thats where we'll start,First thing is have you checked the coolant level in the radiator when engine is cold,make sure it is filled to top,next verify you have coolant in reserve ,Start your van and get it up to normal operation temperature,If your heat gauge on the dash works correctly it should be 190 degrees,Now lift the hood and locate the two heater hoses going into the heater assembly at the fire wall,Both hoses should be hot to hold on to,if both are hot and no heat inside your problem will be the blend air door in heater assembly.
if neither hose is that hot you need to replace the thermostat in the engine to get it up to 195 degrees.
if one hose is hot and one is luke warm then the heater core is blocked and to blame. hope this helps you.