I have a ford areostar,93, after about 20 min lights start blinking on ,off on off?

You dont provide enough info to give you a decent answer but if its your head lights its probably a short. Start the car, pop your hood and find your fuse box. Then grab the wires that run into the fuse box and wiggle them to see if any change occurs. If so, your problem is that the connector from the wire to the box is loose. If not try and find the ground for your head lights and check that also. If that is not the prob, look behind your dash where your head light switch is and wiggle those wires that connect to the switch to see if that changes anything. If thats not it, search high and low for a loose connection. Electrical probs can be a pita, but with some patience you can find the prob.

Headlights; Headlight Switch going Bad or Plugs/Sockets at Headlight need to be replaced!

Heater; Hot Water Valve on Heater Hose, Bad Hoses, Clogged Heater Core, ( Remove Heater Hoses and Back flush Through Return Hose), a/c\Heater Fan Not Working!