 having the same problem
I have a 99 windstar that is doing about the same thing. lost gauges intermintetly, no blinkers, parking lights and tag lights stay on with the key off. after doing alot of looking around I found that there is a chassis computer behind the jack storage compartment. There is 6 main ground connections that I
in the vehicle one under the rear computer, one on the right pillar at the rear lift gate, two on the the driver side under the cover by the hood latch, and two on the the front under the hood around the battery. you can check those and cean them but I found that my chassis computer (rear electronic module) was bad. the computer controls all the switching to the lights it controls door locks the fuel ascending unit. be very carefull how you test you lighting if you put voltage to any ground it can cause allot more problems. The rear electronic module can run around 250-350 dollars but you can find the at junk yards for about 50
make sure you check the number on your computer to make sure you get the right one it should start with a XF2T- and go into some other letters and numbers depending on how many options your van has. If you need the wiring diagram i may be able to email it to you. hope this helps | 
