I have a 1990 f-150 4.9 5 speed. The temp gauge doesn't work. I've seen it move once while plowing, but only like a few milimeter. not even to the normal mark. The sending unit should be on the left side of the motor as you look at it from outside the vehicle. Under the exaust manifold near number 6. I've pulled the wire and put it back on. I don't believe it's a wiring problem, but if it is how hard is it to put an aftermarket one in.

 

Are you sure the gauge doesnt work? It could be your thermostat. Aftermarket ones arent hard to do. Put one in my 351 in 15 minutes. The hardest part was wiring in the light for the gauge.

 

Ground that wire you pulled off and it should peg the gauge.
If it does peg, replace the faulty sending unit.

If it doesn't peg then you have a faulty gauge or voltage problem feeding the gauge.
Unground that wire and check for voltage.
no voltage - check for loose wires/connectors in gauge cluster
has voltage - replace gauge

 

ok, I pulled everything apart tonight. I took it for a ride and got it to move alittle, so i know the gauge works now, i'm just going to replave the sending unit.

 

on a nice 80 degree day the upper radiator hose and heater core hoses should
be just about painful to touch. Just think about the time a hot tea or cocoa burned your hand or mouth, the coolant should be the same temp.
Use those wonderful devices you have been blessed with, your hands. Whenever I am checking under the hood I grab the the hoses, check the hose for pressure and temp by squeezing the upper hose.

I am not optimistic about a new sender solving your problem, those senders are not delicate, very well constructed, and last a long time.