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Fuel Gauge Question - 48 Plymouth


Cold Blue

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I know this question has been answered previously - I have searched the Forum until I am blue in the face (no pun intended..) but I cannot find the answer. I have an aftermarket fuel gauge now, hung under the dash. I want to get rid of that fugly thing and use the original. I have purchased a Runtz voltage reducer to go from 12v to 6v for the old gauge. Looking at the back of the original gauge, it has 3 connection points - power from the switch, and studs saying "1" and "2", for the sending unit. But I think I have a problem...The sender in the gas tank only has one wire..it's a replacement....I will bet I have to get a rebuilt original sender that has two wires. Am I right? I sure hope I'm not....

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Check your local parts stores. They have the after market 2 wire fuel senders, or try Andy Bernbaums and order an original. If you go after market, make sure the ohms resistance setting is matched for your car. On the 46-48 plymouths I believe it is 0-22 ohms.

 

Joe Lee 

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2 minutes ago, soth122003 said:

Check your local parts stores. They have the after market 2 wire fuel senders, or try Andy Bernbaums and order an original. If you go after market, make sure the ohms resistance setting is matched for your car. On the 46-48 plymouths I believe it is 0-22 ohms.

 

Joe Lee 

Joe - So I do have to have a 2 wire sending unit? The one wire unit on my car now won't work, right?

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" So I do have to have a 2 wire sending unit? The one wire unit on my car now won't work, right? "    Why don't you try using your one wire sender connected to ether terminal number one or two . Lift the float with your hand and see what happens . You will probably also have to ground the sender . The reason that I say this is because there is an aftermarket sender for the trucks that hooks up to only one of those two terminals marked 1 & 2 . . 

 
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23 minutes ago, Plymouthy Adams said:

it will not work...the impedance is wrong for one, the gauge electrically is designed to pull the needle in both directions at the same time in the two wire thus the split of the 0-30 to gnd via the wiper....

Yep Plymouthy - I examined the dash gauge closely, and I see how it works. There are two coils with the needle between them, and when the current flows the needle is moved by the coils. So I gotta get a two wire sending unit.

 

Oh well, that's the fun of having a vintage car - getting to fix things on it. And not to mention the knowledge, experience, and satisfaction you get when you repair it correctly, and it operates as designed.

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My 39 Plymouth....after buying a nos two wire guage and getting my my original guage working, I couldn't get either guage to register more than 3/4 full or empty while showing 1/4 of a tank. That scenario is after buying the proper new sending unit. So, I set it to show 3/4 of a tank when full and on empty when it is actually empty. I tried everything to remedy the problem.  

I also purchased a nos 38 guage, but it requires a single wire sender.  The car has all new wiring and I retraced and retested the fuel tank wiring and all is good. If anyone knows why I'm getting 3/4 accuracy, let me know.

Edited by Dennis Detweiler
clarity
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9 hours ago, Cold Blue said:

I know this question has been answered previously - I have searched the Forum until I am blue in the face (no pun intended..) but I cannot find the answer. I have an aftermarket fuel gauge now, hung under the dash. I want to get rid of that fugly thing and use the original. I have purchased a Runtz voltage reducer to go from 12v to 6v for the old gauge. Looking at the back of the original gauge, it has 3 connection points - power from the switch, and studs saying "1" and "2", for the sending unit. But I think I have a problem...The sender in the gas tank only has one wire..it's a replacement....I will bet I have to get a rebuilt original sender that has two wires. Am I right? I sure hope I'm not....

I've been running 12 volts to my gas gauge for over 10 years. No problem. Originally bought the Runtz reducer and it quit working about a week or two later. It's been working on 12 volts ever since.

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the use of 12 volts has been proven for years...HOWEVER though it will work this way, it will not be without some side effects....accuracy will be there...but the gauge more than not will have a flickering needle and a bit rapid change in needle position.   This is due to the fact that the 6 volt regulator that is built into the gauge is opening and closing at a faster rate.  Why folks do not do what the factory did in 1956 when voltage went to 12 and gauges stayed 6 is beyond me...simple fix, rock solid app and cheap...will power two gauges with no problem.

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7 hours ago, Plymouthy Adams said:

the use of 12 volts has been proven for years...HOWEVER though it will work this way, it will not be without some side effects....accuracy will be there...but the gauge more than not will have a flickering needle and a bit rapid change in needle position.   This is due to the fact that the 6 volt regulator that is built into the gauge is opening and closing at a faster rate.  Why folks do not do what the factory did in 1956 when voltage went to 12 and gauges stayed 6 is beyond me...simple fix, rock solid app and cheap...will power two gauges with no problem.

Excuse my ignorance Plymouthy - but what did the factory do in 1956? You say voltage went to 12 and gauges stayed at 6...there was a simple fix with a rock solid application. What was the app that powered two gauges with no problem? The Runtz reducer? Thanks!

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the CVR     if just putting a resistor in line would have sufficed, the factory would have done that as it would have been cheap cheap cheap....the CVR is designed to maintain the output of correct voltage to the gauges across the spectrum of 12 volt battery and its related charging system...very effective....you can also make  your own CVR from a semi complicated circuit of power transistor regulator, filters, trim resistors and adjust the output voltage for your needs.  They are also very inexpensive on places like e-bay, you can go to forums and such and get ways to make these using simple zeneer diodes....the list goes on....do some reading on the CVR....as an aside to those with the two wire....I recommend an inline voltage regulator and adjust it to 7.2 to feed the gauge and this will in turn allow the internal voltage regulator built into the gauge to do its job of maintain 5 volts to the gauge movement...The CVRs are a pulsed voltage out and I do not recommend them for two wire guage, they were applied at change of 6 to 12 era as the two wire was out of use by then.  Knowing your system requirement is step one...meeting that requirement is step two...

Edited by Plymouthy Adams
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