Does the fuel & oil psi gauge work?
If so then it could be a few things, bad sender, bad wiring, bad gauge.
To test wiring & gauge find the temp sender and make sure the wire is on it tight for a start, motor up to temp and see if the gauge works with key on.
If not pull the wire off the sender and short to ground. Turn the key on and the gauge should start to move to hot.
Another way to test and was posted over in the 80-86 area, swap the oil psi & temp wires to senders may need long jumper wires to do this and see if the gauges move when motor is running. if the temp sender is bad the oil psi gauge will not move.
If you find the temp gauge will not move with either test above will need to start checking the wiring from sender to gauge.

There may be a way to check the gauge but I don't know it for Ford trucks. I know of pulling the gauge not working and using a 1.5 volt batt put it across the gauge posts and see if the gauge moves. If it moves gauge is good if not bad gauge.
From that point you would know where to start looking to fix it.
Dave ----

 

I had the same issue and it was the sender. I picked one up at O'Reillys for a few bucks. It threaded right into the top of the motor (on my 360) but I did have to drain some coolant out of the radiator first. The sender is lower than the top of the radiator. Someone else here may know if that's the same for a 302 but I imagine it is.

 

 

Power for that circuit comes from the Ignition Switch when it is in the "ACCY. ONLY", "ACCY, & COIL" and "COIL, START & PROVE OUT" positions. Best to test this circuit in "ACCY. ONLY" (to protect your points, if you have them).
Disregard - Power from the "A" pin of the Ignition Switch goes to one of the resistor wires and from there to the Alternator gauge - disregard.
Disregard - Power from the "A" pin also goes to the accessories (Windshield Wipers/Washer, Radio, etc.) and feeds the fuse for the back-up lights as well as the fuse for the heater system's switch - disregard.
Pay attention now - Power is also supplied through the Instrument Cluster Connector, and goes to the Instrument Cluster Constant Voltage Regulator. This provides regulated power to the Fuel and Temperature gauges. The other side of the Temperature Gauge goes to a three-pin connector under the dash. This connector has three wires on one side of the connector (Pink, White with Red stripe and Red with White stripe), and four wires on the other side of the connector (those three and Blue). From this connector, it goes through the firewall and connects to the Water Temperature Sender (Red with White stripe), the Oil Pressure Sender (White with Red stripe) and the Ignition Coil (Pink). Even though the power comes from the Gauge to the Sender, the Sender actually controls what the Gauge shows. The Water Temperature Sender acts as a variable ground; full ground should be maximum indicator on the Gauge.

If your Gauge reads full hot, check for shorts; if it doesn't move at all, check for opens. Obvious question: Is the Sender plugged in?

If your Fuel Gauge works, then the Instrument Cluster Constant Voltage Regulator is probably working correctly.

Changing out the Sender is a cheap and easy job, just temporarily drain some of the coolant out before you remove the Sender.

That three-wire bundle rests on the top of the intake manifold and over time the engine heat can make the wire insulation brittle. If any of the wire in your three-wire bundle has brittle insulation, splice a new wire in, re-wrap it with new electrical tape and consider adding a cheap heat jacket of some kind. I wouldn't bother trying to replace the entire wire bundle, it's extremely awkward to get the connector through the firewall grommet.

 

 

In every vehicle I have ever driven, what you just described is a working temperature gauge.

 

It may be that the PO (Previous Owner) removed the thermostat. That could be the reason the gauge only moves a little. Mine will move almost to the HOT area, if I'm sitting still for a long period (30 min).