Fuel tank and gauge

[Carl-Gustav]

Hi guys!

 

Ok, this is a tough one for ya ?

 

My Chrysler New Yorker has 6V positiv ground. My fuel gauge hasn't been working for years and I don't get the instructions in the manual for testing the gauge ? ... Old stuff, probably not going to work... So, I decided to install a 12V gauge and sender (I have a 12V battery in the back for the soundsystem)...BUT ? the tank is in contact with the car so it's grounded 6V positiv... Will the car and my house explode ? if the new 12V sender is grounded as instructed to NEG 12V and touches the POS 6V grounded tank?! 

Was this question fussy enough to make you confused? ?

 

My plan is to isolate the sender as much as possible, even the screw holes though they will be grounded to the tank.... 

 

Any ideas or don'ts?

By the way, I'm not planning to convert the whole car to 12V.... 

 

//Carl

 

[wagoneer]

Hi Carl, 

  I don't think it will matter much that they are grounded to the body but I'm not an expert in this topic per se. 

Rather, I'm interested that you have a 12v battery in your vehicle. How are you charging this battery, and what do you have connected to it?

 

[Carl-Gustav]

Hi ?

 

Well, let's see what other members think of it ?

 

I was thinking of putting a step up converter but as I already had a solar panel charger for 12V I tried it and it works amazingly well ? 

 

I have a BOSS MC900B car amp with built-in Bluetooth and usb-charger ? works really well. 

 

[allbizz49]

Sender measures ohms, not volts. The light in your gauge is 6 volt though. 

[Carl-Gustav]

Yes, I know that the sender measures ohms and the new gauge is for 12V. But the thing is that the sender has to be grounded according to the manual and I can't ground it to the vehicle or tank though they are POS 6V .... Do you follow my consern? ?

[DonaldSmith]

Let's see, 6 volt positive ground battery and circuit, and a separate 12 volt positive ground battery and circuit.   I had something like that for a while, for a 12 volt pusher fan, but I had no automatic way of charging the 12 volt battery, so I now have a 6 volt fan and a step-up for 12 volt electronics. 

 

Each circuit has one side grounded, and the other side insulated (wires insulated, connections separated by air from anything else).  Everything is OK, won't blow up.

But if you connect a volt meter from the "live" side of one circuit to the "live" side of the other circuit, the meter will read 18 volts.  

[Carl-Gustav]

Hmmm....

 

Look at the drawing ? ... My question is basecly, what if I don't get it right and the new sensor ground (12V NEG) touches the tank/car that is grounded 6V POS?.....

 

 

[Los_Control]

Congratulations,  you just found something to study and learn.

Not trying to be a arse ... just saying you need to learn this. The info is available and you are in the right place.

 

When I ordered my new tank and sending unit from Tanks   The lady answering the phone asked questions ... I was very specific about being 6 volt + ground.

She scolded me like a old school marm and said it did not matter. Just saying she sold the units for years and she said it does not matter 6 or 12 or + or - the sending unit will work for my application.

Not saying she was bossy, she just really sounded confident in her opinion.

 

My only point is, the fuel gauge on some cars do not depend on 6 or 12 volt or + /- ground.

Some cars like maybe your Chrysler have 2 wires going to the sending unit. And I have no clue about these sending units ...  You need to study this a bit.

I even think it matters on a Ford or a chevy, you need to add a reducer to drop it from 12 volt to 6 volt.

Your 12 volt battery in the trunk probably should not be connected to your fuel sending unit.

[RobertKB]

There are reproduction new gas tank sending units out there for the 6V Mopars including your car. NOS gas gauges appear all the time for our cars on eBay. I would look for one of those and a new sending unit. Don’t mix 6V and 12V if you don’t have to. 

[Carl-Gustav]

Sure, I've seen them out there but as usual I have to order it from the states or China and costs me to much.... I'm trying a cheaper version...my plan is to have the 12V gauge in the glove compartment, don't have to see it all the time ?

 

The old sending unit is getting out and the new one installed in the same hole, there of the grounding matter...

 

 

[Andydodge]

I dunno if this is any help but my 1940 Dodge has run at 12 volts since I installed the Poly V8 in the early 70's......the fuel gauge has had a standard voltage drop resistor and it is reasonably accurate although once it gets down to 1/4 full I start to make sure it gets filled soon after........andyd

[knuckleharley]

I have read this whole thread,and am more confused now about this issue than I was before I started reading.

 

Chemo brain,or are their other people just as confused?

 

The one thing I DO understand is the simple principle beaten into my thick skull when I was a kid,namely "The KISS principle",which stands for "Keep It Simple,Stoopid".

 

My suggestion,and worth every dollar it cost you,is to spend the damn money and buy a NOS  or repo 6 volt sending unit. Preferably one NOT made in China if at all possible.

 

You say they are expensive to buy and have shipped to you,but how much do you have in your car? How much will you love if it burns to the ground?

 

Yeah,some of the electrical geniuses here know how to get around all this danger,but if you ain't one of them,why take the chance?

 

BTW,still thinking that electrical systems are the work of the devil,I carry a fire extinguisher in my P-15 couple,and everything in it is 12 Volt. While driving home one day I turned a 90 degree corner,and the 4brl carb farted and caught fire. I still have a car thanks to that 10-15 dollar item.

 

 

Edited July 22, 2021 by knuckleharley

[Carl-Gustav]

Why so confused? I thought it was crystal clear ?

 

I get it, many of you don't think it's a good idea to mix 6 and 12 volts. Of course not but it's not easy to find the right gauges and sending units over here. You can probably go to the local farmacy and find something over there ?... 

 

But to find a 6volts Neg ground gauge and a sending unit that fits the original hole...hmmm.... ?.... Not interested in "new" stock from 1945 either... 

 

By the way, I always have 2 fire extinguishers and a "blanket" in the car at all times ?

[Carl-Gustav]

7 hours ago, knuckleharley said:

I have read this whole thread,and am more confused now about this issue than I was before I started reading.

 

Chemo brain,or are their other people just as confused?

 

The one thing I DO understand is the simple principle beaten into my thick skull when I was a kid,namely "The KISS principle",which stands for "Keep It Simple,Stoopid".

 

My suggestion,and worth every dollar it cost you,is to spend the damn money and buy a NOS  or repo 6 volt sending unit. Preferably one NOT made in China if at all possible.

 

You say they are expensive to buy and have shipped to you,but how much do you have in your car? How much will you love if it burns to the ground?

 

Yeah,some of the electrical geniuses here know how to get around all this danger,but if you ain't one of them,why take the chance?

 

BTW,still thinking that electrical systems are the work of the devil,I carry a fire extinguisher in my P-15 couple,and everything in it is 12 Volt. While driving home one day I turned a 90 degree corner,and the 4brl carb farted and caught fire. I still have a car thanks to that 10-15 dollar item.

 

 

You are right!

 

Better safe then sorry ?

[Merle Coggins]

I have a 6v to 12v converter in my truck to give me 12 volts for my modern radio. It also allowed me to put in a couple of 12v power outlets for my GPS and etc. According to the instructions for wiring it up it is designed to share the chassis for grounding. 6v pos ground in, 12v negative ground out sharing the same ground plane through the cab. It seems to work OK. 

[Sniper]

If you are just sharing the ground it's not an issue. 

[Carl-Gustav]

I'm looking out for a 6v gauge instead now ? Well, back to the question is that they wouldn't share grounds though the chassis and sender unit would get 6volt POS and the gauge would have 12volt +/-..... Unless I tried to isolate the sender completely for the 12volt neg ? feels a little risky don't you think?

 

 

 

[Sniper]

The sending unit on the aftermarket gauge is nothing more than a variable resistor.  The gauge would get 12v for the supply and it's return goes thru the sender.  It is not a problem to use the chassis as the return for the 6v positive ground vehicle system AND the 12v negative ground gauge as long as they do not also share the supply side.   In other words keep the 12 positive supply separate from the 6v negative supply and you are good.  No need to isolate the sender.

 

When I was in the military as an electronics tech I worked on many pieces of gear that have multiple supply voltages and polarities, but they all shared the ground.  Even the AC used the same ground as the DC.  As they used to say in class, ground is ground the whole world round.