1990 LTD Country Squire. Blower only runs on high

check the resister its by the blower motor use a muitimeter check voltage when switching thru speeds

Find temp. sending unit on engine. If one wire type ground that wire to good engine ground, with key on gauge should go all the way to hot. If it does replace faulty sender. If it doesn't than you have bad gauge, wire or connection. ( If replacing sender, make sure engine is cold. remove radiator cap to releave pressure and you will loose antifreeze when it comes out install new one quickly and don't use teflon tape as this needs to be able to ground to engine.)

Remove the starter and test it by applying power directly from the battery using jumper cables. If it doesn't spin, replace or rebuild the starter.

that could be the water valve that is controlled by the hot/cold knob on teh heater control, Have someone turn the knob to cold and then hot and see if you can see the valve turn.

Feel the inlet and outlet heater core hoses. They should be about the same temp when the engine is warmed up.

just snug the nut up but not so tight the rotor will not turn. just snug enough so the rotor turns without being loose. have a good one!!

The front of the engine. Look where the radiator hoses are connected.

Did you change the flasher relay? Do the 4 ways work?

Your engine has "throttle body injection".

you can just buy a addapter plug

Sounds like a fuel pump causing noise. If the noise is still present with the key off then the fuel pump relay is stuck causing the battery to die.