Ok fellas, on my 49 ford coupe, when it was my dad's, he had the car fully rewired for 12v. I am finishing the job currently. I added a ground to the sending unit being it has a poly gas tank, and I have a 12v to 6v reducer from Dennis carpenter. All said and done, there is 5 gallons of gas in the tank, and when I turn on the key, the gauge goes up to 3/4 tank. I followed the wiring diagram from the green book and I have the positive on the correct post and the sending unit wire on the corresponding post as well. What could be my issue? No smoke show so I did something right at least. Lol. Thank you!
I'm no expert Assuming the float height is correct for the tank, possibly the sender resistance value (ohms), is incompatible for use with that fuel gauge...? Wiring sounds correct, from what you describe. Good luck!
I am no wiring genius by any means but I believe this is correct from what i've researched. Thankfully nothing went up and smoke when I powered everything up. Lol
I'd make sure the sending unit is right for the tank. If you look up the poly tanks they list 17 gallon capacity- deeper than stock. Looks like they have a recessed area for the sending unit, but you never know how correct that is.
If you remove the sender but leave it electrically connected, you may be able to bend the float arm to suit the tank, and adust it while someone reads the guage.
Tanks inc (sells gas tanks and accessories) has a inline device called Meter Match that lets you calibrate sender with gas guage. This might help.
When doing a 12 v conversion on a car with a 6v gage and sender I use a small voltage regulator from a late 50s to mid 60s ford, Mopar in those years also used them. It,s a small rectangle on the back of the instrument panel that feeds 6 to9 volts to the gages and works by a bi-metal spring with contact points that open and close to regulate the voltage.
What kind of voltage reducer are you using? If it is just a resistor, that is the problem. You need to use a solid state reducer, otherwise the voltage at the gauge will be higher than 6v. Check for 6v at the gauge.
some good advice here yes with the sender out of the tank and the wires hooked up'move full to empty & watch the Guage. if it wont work out of the tank no amount of adjusting the float will make it work; next you will have to adjust depth & length of the arm may have to cut it of & rebend the L on the end or curve the rod, if using the ford type pulsating reducer I believe you need to check volts with a analog meter as a digital won,t read
It is the one from Dennis carpenter that you can use with multiple gauges instead of using the rundt style for each gauge. I hooked it up per instructions and via green book for the positive post and post for signal from sendingnunit.
Corvette Central and possibly others supply an adjustable resistor to be installed in the sender wire for a temperature gauge to adjust the gauge position. I have found it will work for a fuel gauge also.
If the gauge will not read correctly when you test it out of the tank, it probably has the wrong ohm range for the sender that doesn't match the gauge. See chart below. First number is empty, second number is full reading.
^^^^^^^ This. Most aftermarket gas gauge senders are made for the GM Ohms range. Unless specifically ordered for another range.
So, another guess from an admittedly electrically challenged individual........Isn't the ground on the Ford 6volt stuff............positive? Is it possible to reverse the connections and get a 1/4 instead of 3/4 reading?
The fuel gauge doesn’t care about direction of current flow only the magnitude, reversing the polarity won’t make any difference to the gauge reading.
I'm just going to get a new sending unit from shoebox central. It's for 6 or 12v , made for the poly tank and will work with original gauge
To get the gauge to read mostly correctly on my '40 with a poly tank I had to throw the aftermarket sender away. They are not compatible with an original Ford gauge. Then made an adapter to go from the modern flange on the tank to the old Ford sending unit and installed a NOS sender. It took a lot of fooling around with the float arm, float and the adjustment on the sender but I have a fuel gauge that works pretty well from Full to 1/2 and is very accurate below that where it counts... The Dennis Carpenter voltage reducer has worked well for me.
Or you could build a voltage reducer yourself. I did and put them on my 49 Buick. Been working for 5 years now.
Before you bolt it all together, try a dry run on the new sender. Run the feed and connect a ground jumper. Hold it straight up (empty) then flip it over so the float is at the top of it's travel (full). Verify it's making the gauge read properly. Understand the tank can limit travel and that some bending/adjusting may be needed.
I ran into an issue on 48 truck , I used voltage reducer fame 60s era Furd all the same car and truck . Remember 6V system was + ground 12 V system is - ground
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