'64 F100, 292 V8, Manual 4spd, 4X4, All Stock.
Just tooling down the road, minding my own business. Choke set about 10% on 'cause just started truck and I'm letting it warm up. All of the sudden both Fuel and Temp guage start wavering back and forth from full on to full off. Never seen them reach either full position before. After about 10 seconds I smell something burning so I pull over. Truck still running fine, but right before I pulled over both guages went to full off position and don't move any more, period. Couldn't find any burnt wiring and truck running fine so I started back up and continued on my fishing trip (Priority No. 1)
Drove the rest of the day (2.5hrs out, 2.5hrs back) when I got home I took out the panel to troubleshoot the problem. Here is what I found:

1. With key on I've got 12v on one side of the inst. regulator but no 5v (approx) on the other side.

2. Both guages measure infinite resistance across the terminals (I think this isn't right).

3. Both sending units, especially the fuel are working fine. I substituted a 5v semiconductor regulator in place of the Ford one and still no movement on the guages.

4. I removed the fuel guage from the panel and looked inside. I believe the tiny wire inside is fried looks like a tiny heating coil to me...So it should have LOW resistance but it doesn't.

My theory is the regulator died and exposed both guages to higher voltage and fried them ? Please let me know if I'm on the right track...

How can I repair this without buying new guages ? Aren't they expensive ? Plus won't I need new senders ?

On the plus side I caught a ton of Smallies and truck ran fine all day...

 

I'd start with replaceing the regulator, as I am almost certain that it is fried, as you suppose. I am not so certain what the resistance accross the fuel and temp guages should be -- they move by producing heat in that little coil. If they are fried and have infinite resistance (evidence of discontinuity, thus "fried"), then they should not damage the new regulator, IMHO

As to replacement guages -- I do not know that I have ever seen them, but instrument clusters go for 5 to 15 bucks on eBay. Pick up some used ones and hope for the best. The replacement guages USED to be available at stock parts places -- I remember the temp guage going out as a kid and my father replaced it with one that had fewer markings. Still is in there to this day. But I have no idea if such a beast is still available -- I doubt it.

 

First some information:

1. Both Fuel and Temp Gauges should read about 12-13 ohms across the terminals in the back. This is a tiny coil that heats and moves the needle indicator.

2. Both Fuel and Temp sensor move from about 10 ohms full scale to about 170 ohms near empty (Cold). Thus the regulator puts about 5 volt DC across this little circuit, and as the sensor resistance changes, the needle pointer is deflected. So using this information you can troubleshoot the gauge circuit pretty easily.

3. I used a modern semiconductor 5 volt regulator instead of the $35 Ford one. Seems to work fine once I replaced both gauges.

 

Now that I've run the truck a couple weeks I really like the way this instrument voltage regulator works. The gauges have never been this steady and reliable. I keep it adjusted to about 5 VDC. The temp gauge always registers about 150 degrees whereas before I never got much of a reading on it at all. Maybe slightly over 115 degrees. I knew that wasn't right. And the gas gauge finally reads full for pete's sake.

 

Where did you get the regulator? I just fried may third OEM. 35 bucks for a replacement that only lasts a year is a rip off.

 

Bought it at the local Electronics Supply (Norvac) store plus all the parts for $10. It does get hot so buy the heat sink. My other FoMoCo regulator had a coil in series with the input Voltage so I re-used that. I keep the Vreg adjusted to about 4.9v, works good so far...

Sure with I had a 12v 30 amp regulator just like this...!!