Hi Desert XL and Action+1,
I would first check to make sure the voltage regulator for the fuel gauge is working first before messing with the sender as it's under the dash. The voltage regulator crudely regulates by switching B+ on and off rather quickly giving a rough 5 volts if you integrate the area of the voltage of time spent on with respect to total time of one cycle or the period. In other words it's just a really fast flashing thermal turn signal flasher type device. This rough 5 volt output is what powers the fuel gauge. So the fuel gauge gets this "regulated" +5V on one terminal and the other terminal goes to a variable resistor in the fuel tank that's connect to a float that rides on the level of fuel. The other end of the variable resistor or in this case a rheostat is grounded (behind the back seat) to complete the fuel gauge circuit. Measuring resistance of the sender should yield, If I remember right, 10 ohms is full, 73 ohms is empty and 23 ohms is half full or half empty depending on your point of view of the world.
A couple quick checks for the fuel level gauge is check for the +5 volts on one terminal of the fuel gauge, if you have that, then unplug the electrical connector at the fuel tank and ground the wire going to the sender in the plug, that should cause the fuel gauge to read past "F"ull. If that happens it's a pretty good guess the gauge and the wiring is good up to that point and the problem lies within the sender inside the fuel tank. However it doesn't mean the fuel gauge is accurate.
The best way to test for true accuracy of the gauge is buy the 3 resistors I noted (a 10, 23, and 73 ohm 5 watt) and sub each one in at the connector normally on the tank and see what the fuel gauge reads. If you look really closely at the fuel gauge above the letters F and E there are two tiny dots. When substituting the fixed resistor(s) in place for Empty and Full the needle should be within the two dots or resting on one of them depending on which resistor is substituted. And of course the meter should read half for the 23 ohm and there are no calibration marks for that, but is rather a gross calibration check.
Just a note on the sender (variable resistor/rheostat) inside the tank. If it's found to be at fault, you may wish to look for a good used one or an NOS one. The reproductions are terrible as I bought one a couple years back.
On the topic of the dash lights. Have you tried to turn the headlamp switch with the parking/running lamps on or headlamps on? That dims the dash lights and also turns on the dome lamp if rotated all the way to the left. That also is a rheostat and the contacts get dirty to dim the dash lamps. There is a 3 amp stubby fuse in the fuse block that feeds the dash lamps, check that to make sure it's not blown or has dirty contacts. Again that fuse only gets power if the headlamp switch is pulled out 1 or 2 notches (parking/running lamps or headlamps position) and with the knob turned all the way to the left just before the detent that turns on the interior lamps.
The clock is most likely exactly what Action pointed out. It could also be on rare occasion that it has truly blown off the contacts off the rewind coil by normal long running. Every 20-40 seconds the rewind mechanism activates on these old clocks and it's a high current short duration pulse that slaps the mainspring to wind a little. Since it's just a big solenoid on a set of points and Ford chose not to use a capacitor or diode across the points they arc rather severely every time (20-40 seconds) the rewind is called for use. This blows minute chunks of points away every time and eventually there's nothing left.
You have a couple of choices when it comes to the clock. You can try to find an NOS one and just see if it works, but an NOS one will probably be 100-300 dollars and is still a gamble as it's NOS and all the lube is dried out in it. Even if it does work it will erode the points unless a diode is placed across the points in reverse bias to act a free wheeling diode and alleviate the arcing. This takes a little skill with soldering to achieve (been there done that). Or your last choice is to send your clock out for a quartz conversion. This is also pretty pricey but if done right will last a lifetime. I did a unique quartz conversion on my 1973 Chevrolet full size cars' clock over 20 years ago and it's still working to this day keeping perfect time. I cannot vouch for others work so do your research before you commit to a particular service.
Hope that helps a little.
Thank you Sirs for your excellent knowledge again. Actually with the Dash lamps, they are coming on, so the bulbs are ok when I pull out the headlamp switch, however they are very faint and dim, can hardly see them illuminated and go off intermittently when the headlamp switch is rotated either to the left or right.
Is the brightness supposed to increase when the headlamp switch is rotated all the way to right (or left)?
I've changed the 3amp fuse and cleaned the contacts. Could this be a dirty - faulty headlamp switch or contacts behind it?
Would I have to remove the instrument panel to check it?
Thanks Larry M