All gauge goes crazy on my 1990 taurus what is the cause for this problem

have your alternator tested

If your "goes crazy" means what I think it does, it's unlikely to be a float. That failure mode is "empty" all the time.
I'd say either sensor or wire between sensor and gauge.

Ford 150 Van No Start No Crank Same problem aftermarket remote start problem !
Watch the second part too . Do you know what a wiring diagram is ? Look under dash or the hood an see where the remote start is hooked up , what wires ! You can find a wiring diagram here at http://www.bbbind.com/free_tsb.html Enter the vehicle info. year , make , model an engine size . Under system click on engine , then under subsystem click on starting . Click the search button , then on blue link . You'll see all the componets in the starter circuit .

Your alternator may be on it's last leg. Start the car and while the car is running, remove the negative cable from the battery. If the car dies, the alternator is no longer working. If you have a volt meter, put the meter on the battery positive and negative. You should read 13.8 - 14.2. If it doesn't show this, and reads under that, your alternator is not charging enough to keep your accessories going.

Try a new oil sending unit. The right way is to hook up a mechanical oil pressure gauge and see if it mimics what you OEM gauge is reading.

sounds like air in system

you have a fuel pump problem it was shorting for some reason hence the gauge going crazy from the float circuit being shorted. your fuel pump is on it's last leg have it replace this will solve the problem. please rate this

check your cluster

Switch ig. on, ground the sender unit wire for about 3 seconds see if the temp. gauge moves, if so change sender unit, if not then it is a faulty gauge reader.

You probably have a faulty sensor at the transmission.

Go to your local parts store, and they can give you the part and how to install it. It's pretty easy.