I converted my 46 to 12 volts, and All I needed was a little thing called a Runtz for the gas gauge that I bought from Speedway motors. I also used a GM single wire alternator.

From information I received from Park Waldrop a few years ago, if I remember right, the '51's and later needed the small dash regulator. I have a spare set of '51 dash gauges with the original regulator still attached. I wish it would be that simple as to put a resistor in line for the gauge(s). I know if I call Dennis Carpenter Ford they'll want to send me another one but I'm inclined to eat the cost and try something different. Terry

The Runtz from Speedway cost $18.99 I just looked it up. Attaches right to the gauge between the gauge wire and gauge. I have a direct temp gauge so I didn't use a Runz on that gauge. The only other change besides all of the bulbs was to swap out the heater blower motor for a 12 volt one from O'Reillys.

Took the '51 out for a drive and the gas gauge suddenly started working but the temp gauge didn't until I made a hard u-turn at a construction site....then they both worked for about a minute. The gas gauge still works but the temp gauge quit again. I'm thinking a ground issue? Or maybe the temp sender? They're both connected to the same voltage regulator so the regulator must be working. Any ideas? Terry

It is more likely an issue with the senders, or the wiring from senders to the gauges. The little constant 5.5 volt regulator merely regulates the power coming to the gauges from the ignition switch. So if the wire from ignition switch to the 5.5 V instrument voltage regulator is loose at either end, or is grounding due to bad insulation, then yes that can cause a non functioning / intermittent functioning issue. The original fuel senders are notorious for having issues due to the age of the variable resistor coil and brass brush being corroded, covered in gummy residue, etc. Likewise the temp sender that screws into the cylinder head can be unreliable from age, or poor ground through the threads.
I converted my '53 Hornet to 12 V negative ground in 1986,. It has the original 5.5 V instrument voltage regulator and it is still working fine. I did have to replace both senders at different points in time, as well as re wire them, and put a ground wire to gas tank sender from frame after I had painted the gas tank and the straps holding it. The new paint was acting as an insulator, thus no ground to the sender. Originally the factory installed the gas tanks and straps unpainted. They were silver zinc galvanized when new, thus the ground could get to the sending unit.

I didn't take the temp sender out but I did turn it a half turn in the head thinking it might make better contact. Still no go. I'll trace the wire back to the gauges and if I can't determine the problem, I'll try to find another temp sender. I have another set of gauges from a '51 and it still has the regulator attached so I'm covered on that end and I thought I had a spare sender but I can't find it at the moment...I'll dig a little deeper. Thanks Terry

UPDATE. I bought a Standard VRC-604 regulator and it worked on the gas gauge but not on the temp gauge. When the ignition switch was turned on after the car had been warmed up, the temp gauge would sweep up to the middle position but slowly settle back down to the cold mark. I tried grounding the gauges, put in the extra set of gauges, same thing. I finally took the gauge cluster out, took out the link that connects the two gauges together and ran separate wires to each gauge. I kept the VRC-604 for the gas gauge but bought a Runtz (thanks Ed) for the temp gauge and hallelujah! it worked. I did not mount the Runtz on the back of the gauge per the instructions, but at the bottom of the dash next to the VRC in case I have to change anything. Now all I have to do is tidy up the wiring a bit. Terry

Terry, we have the correct new temp.sending unit. These do go bad. We also always recommend to purchase an infered thermometer. Once the engine has come completely up to operating temperature, take the infered and check the actual temp at the cyl.head/sending unit and where it reads on the dash. It is very common to find the dash gauge reads between 1/2 and 3/4's when the actual engine temp is only 160-170 degrees. This usually means on a warm day, as the engine runs a little hotter, the dash gauge appears to read between 3/4's and up, but the actual temp is only 185-200. That temp is not close to boil at all, but many think the engine is ready to overheat... An inexpensive infered in the glove box is a great tool to have, gives a piece of mind, and can be used to simply check other components on your car. When traveling, and stop for food or fuel, you can do a quick walk around your car and check each wheel/rim for abnormal heat. Once you have/create a reference of what normal on your vehicle is front and back, this makes a quick and simple inspection for any potential concerns or problems that might be occurring.
This applies to any vintage vehicle, Ford, GM, Chrysler, etc,...

Thanks, Doug. I do have an infered thermometer that I used to dial in the temp gauge. To get it to read as close as possible, I put a 10 ohm, 10 watt resistor in line from the sending unit...I did this several years ago. According to my math, a 13 ohm, 10 watt resistor would have been spot on but Digitkey didn't have that resistor. It reads a hair over the center 160 degree mark when totally warmed up. I picked up a NOS sender from Jackson Auto here in town- he specializes in NOS older car parts and he sold me a Shurhit WT-326 sender (made by Borg Warner) for 10 bucks. I put it in and it reads slightly below the center mark with the head temp at 152 degrees with the resistor still in place....close to the first senders readings. The cars been put away for the winter so I'll get to know how close the readings are when I take it out next spring. I tried to take the regulator that's used in Fords (Dennis Carpenters D-10800) apart but destroyed it trying to break away the encased epoxy so I'll never know why they were failing. Terry