1955 Ford Part 114: 12 Volt to 6 Volt Fuel Gauge and Sender
Fuel Gauge and Sender
Since we have the car up on jack stands to do a little work here and there, I thought it best to take some time to tackle the fuel gauge. This 55 Ford Fairlane was switched over to a 12 volt system long before I got a hold of the car back in the early 90's. One of my first learning experiences about voltage took place when as an ignorant teenager I tried to get the original 6 volt clock working. Class was certainly in session when I got upside down, legs over the front seat backs, with my head, arms, and hands up under the dash. It was not long before my mother came out on the front porch to see what was going on and why Dan was tinkering with the Ford parked on the street in front of our house. Just at the time she came out the front door smoke was billowing out the open passenger door window. I got some wires crossed up somewhere and some sparks flew, insulation started melting, and I was hustling to get out from under there! A long time has past since that day, and I would like to think I have learned a little bit about automotive wiring; however, there are times when things can get a little baffling on this old Ford.
The 55 Ford Fairlane at a CVA convention in Fredericksburg, Virginia, summer of 1991
The 55 Ford Fairlane on the trailer for the trip that brought it out of storage
When I drove the car as a teenager, the fuel gauge worked somewhat, but it always showed 1/8th of a tank more on the gauge than what was present in the fuel tank. In other words, the tank could be completely empty but the gauge would read 1/8th. This was not necessarily a problem - I just learned to make adjustments to the fill-up schedule. The last time the tank was out of the car (roughly 2008) I took it to a local radiator shop in Winchester, Virginia. The shop took the tank, cleaned it out with industrial grade solvent/chemicals to remove all corrosion, and then sealed the tank. They also checked the sender, fitted a new arm and float, installed a new pickup tube, and told me I was good to go. That was quite a few years ago when I had just got the car out of my parent's garage and was getting the car back into a somewhat drive-able shape. I honestly cannot remember if the sender was original to the time I was a teenager or if I had replaced it at some point.
At any rate, it was time to get the fuel gauge working again. If you know automotive history, 1955 was the final year for many US manufacturers to use 6 volt systems. In 1956, Ford went to 12 volt systems and never looked back of course. What makes all of this a challenge are the following items...
There is an obvious difference in 6 volt and 12 volt systems. (my 55 ford is now a 12 volt system)
Ford used 12 volt gauges in 1956, and then in 1957 went back to 6 volt gauges. The systems were 12 volts but voltage reducers were used for gauges from 1957 on I am told.
There is a debate back and forth among enthusiasts concerning whether or not the gauges are voltage sensitive (some say you have to swap out the gauges and sender for a 12 volt model year, others say there is no problem at all - use as is).
I am not particularly clear on how my new wiring harness will respond - there is certainly a circuit for the gauges in the system however.
The first order of business was to make sure that both the current gauge and sender were in working order.
EDIT - This post began in the spring of 2022 and was put on hold until September of the same year, so there were several months between entries. I did end up making a complete video that includes the footage recorded in the spring and of course the end result just a day or two before the blog entry was finished.
The ground terminal on the fuel sender was missing its lead.
When I was able to tackle this project again, I went back to the trunk of the car to make sure the sender was working correctly. A special note here would be to add that since the sender and gauge work together on a "resistance to ground," BOTH the gauge and the sender need to have clean, good grounds to the electrical system of the car. (The video below shows my correction on this - the sender was grounding to the car's vehicle electrical system via the gas tank straps, but the ground terminal on the sender was missing its lead.)
Installing a new 150 mph speedometer face plate prompted my work on the fuel gauge...
Believing that I needed to switch the voltage from 12 volts to 6 volts, I purchased a converter pictured below. These converters are available on Amazon, eBay, and the like; and most of them are made offshore. However, after reading up on the small units I discovered that others were having much success. Beyond the classic car market, it seems that the RV world relies upon these little devices as well. I bought another variant that converts either 24 volt or 12 volt down 6 volts full time. Of special note would be the leads - unlike a reducer, that is only wired in line with the positive terminal, the converters must have a ground as shown. Reducers will really heat up, the converters not so much and of course offer much more longevity.
The 12 volt to 6 volt converter was pre-wired for testing.
As the video shows, I first wired up the sender, converter, and gauge all in the trunk just to see what was going on. From what I could tell the sender was working properly, so it was on to the instrument cluster and installation!
After removing the cluster, I used a towel to keep the painted surfaces scratch-free.
In addition to the 150 mph speedometer face plate and the fuel gauge, I also replaced the oil pressure warning light bulb socket. It had fallen out and was lying the black hole behind the dash if you know what I mean. I hooked up a few temporary leads and hit the switch - bingo! We had a good reading on the fuel in the tank. No more guessing game here. Of special note would be the "12 volt" gauge I had purchased from a Thunderbird vendor. (The 55 Ford passenger car shares much in the way of wiring and gauges with a 56 Thunderbird - which shipped with 12 volts.) Either Ford still kept a reducer for their 12 volt Thunderbird in 1956, or this was not a 12 volt gauge and was indeed 6 volts. Whatever the case, 6 volts did the trick!
I will certainly update the blog in the coming months concerning how the 12 volt to 6 volt converter is doing with the fuel gauge. Hopefully, I can take another look at the temperature guage and double up on senders at some point so that both my original and aftermarket gauges will work. One quick note to add - I am thinking that my speedometer needle may now show a more correct reading at speed. The gearing from the transmission was making the speedometer read 10 mph slower than what any GPS device displayed. With my plastic gear in the cable housing I am already maxed on tooth count. This may be further evidence that the transmission I rebuilt came out of a 1955 Thunderbird and not a Mercury. Oh! I did lubricate both the speedometer gear mechanism in the cluster AND the speedometer cable. You may recall that it sounded a little loud during one of my runs at Fast Fords earlier this year. If you would like to see a little more detail on the work with the gauge, then watch the video below.
Video (Fuel Gauge: 12 Volt to 6 Volt Converter)
The Hot Rod Reverend
aka Daniel Jessup