[larrymur1961]

+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.

Cheers

Hi Desert XL and Action
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

 

[larrymur1961]

Thank all of you for the great input. I, too, have dash light problems with 65 Gal convertible. After checking the fuse, then replacing one of the four dash bulbs (bought a bulb pack of varying sizes) I also still do not have any dash illumination despite having interior lights. Oddly, the high beam indicator and turn signal lights in dash do work, so safe to assume on a different circuit. I think my problem lies in the harness itself. Why? - idiot mechanic at a formerly reliable old car specialist caused a near fire in the dash when he routed the hot for choke on new intake manifold, through the accelerator cable hole on the firewall (guessing it was "easier" because lower on the firewall than the accessories through-hole about 6" higher - damn fool). I did not notice because I didn't inspect the work before leaving shop (my mistake) as these guys had done stellar work before. But this guy was new to the outfit. I digress: Didn't take long for the wire to ground in non-grommeted hole. Dash smoking 'n all that. No dash lights since. So, after I repaired most of the damage, fitted a new wire through the correct, grommeted loom hole, all was well with MOST of it .... I am going to have to source NOS harness and re-wire to correct. Idiot no longer working at that garage - he has cost me thousands and they ripped up about $500 labor bill. So far, idiot did the above, destroyed a steering rag joint (cranking on power steering while engine not running), then broke the horn ring trying to prove he installed new contact spring after turn signal cam replacement (had the NOS plastic bag with contact spring he had left on floorboard), and .... drum role .... spun a main bearing due to oil loss when he replaced the oil breather caps with solid, unvented ones causing crankcase pressure to skyrocket and spit the dipstick as well as 2 qts of oil in less than 5 miles. Unfortunately, or fortunately, oil did not hit headers but gushed all over fender wall and down, so no smoking. I had top down so oil smell didn't catch up with my nose till I slowed down. Too late ... I couldn't get her stopped fast enough. I pulled over quickly but damage already done. I was going to get a rebuild anyway but not that day. So this guy, pretending to be a mechanic, took every shortcut he could. Owner of shop whom I consider a friend, ripped up bill and moaned about all the experienced guys aging out with lunkheads like this trying to fill that void. Then, he said he wouldn't blame me if I didn't come back. I took heed of his wisdom. His business is buying, restoring and selling classics. Maybe not for long. Sorry for the tome. Action and DesertXL are correct: Get the shop manual (I have) - you will make mistakes, but not like I did. Each mistake is a learning opportunity - I got mine in spades.

Thanks BarryJ
WOW that's horrendous! How could they possibly screw up like that. Desert XL or Action are correct, we need a service manual for sure, even if it's for reference only or to show the mechanics how to do something, they may not like that telling them how to do their job.
Larry M

 

[Action]

With a 50+ year old vehlce, anything is possible. However, the fuse is either OK or not.
Areas of concern

Just plain old dirt in the instrument light bulbs and diffusers
Poor connections at any point
My guess is the rheostat in the headlight switch. (See picture.) On the white ceramic piece there is a coil. That coil has a contact that drags across it as the coil is being moved.(barely visable) This coil is what makes all of the instrument panel illumination dim or bright. I believe the contact and/or coil are either dirty or not connecting the best.
Removal of the headlight switch and a good cleaning may fix a lot of the issues you are having. I use isopropl alcohol on things like this

Action

Note the headlight switch shown is period correct. However it may not be exact to your vehicle.

 

[larrymur1961]

^^ All the best detail.

Does that model year only have a fuel gauge?
If there are other gauges (coolant) and that other gauge works, the IVR and instrument panel gauges should be good.

Action

thank Desert XL and Action
Yes, it only has a fuel gauge. The clock sounds a bit tricky, a quartz conversion sounds good. I will check on EBay
thanks so much for the detail
Larry M

 

[larrymur1961]

With a 50+ year old vehlce, anything is possible. However, the fuse is either OK or not.
Areas of concern

Just plain old dirt in the instrument light bulbs and diffusers
Poor connections at any point
My guess is the rheostat in the headlight switch. (See picture.) On the white ceramic piece there is a coil. That coil has a contact that drags across it as the coil is being moved.(barely visable) This coil is what makes all of the instrument panel illumination dim or bright. I believe the contact and/or coil are either dirty or not connecting the best.
Removal of the headlight switch and a good cleaning may fix a lot of the issues you are having. I use isopropl alcohol on things like this

Action

Note the headlight switch shown is period correct. However it may not be exact to your vehicle.


View attachment 52612

Thanks Action
Yes you're probably right with this switch illustration, after 50 years, who knows what dirt and build up is in there. Fuse/contact are 100% good.
How do I remove that switch assembly Action? I haven't got my manual yet 🙂
Thanks Larry M