How to disable voltage limiter inside gas gauge?

[Kevin74]

Hello Friends,

I have attached a picture of the back of a 66 Barracuda gas gauge. The voltage limiter that produces 5V for all the other gauges should live inside the gas gauge. I wish to disable or remove the old voltage limiter and instead use a modern 5V solid state regulator. Another FABO has stated that you can disable the internal voltage limiter by blocking its ground connection with electrical tape, hence the tape you see on my gauge.
However, when I test the gauge, I find the 12V terminal shorted to the 5V terminal, which isn’t good. By the way, the gauge works well. I applied 5V to the 5V terminal, then applied 10 Ohms between the Signal terminal to ground. The gauge needle correctly went to Full.

But can anyone advise how to disable or remove the old internal limiter?

Thanks,
Kevin

 

[my68barracuda]

Google. RTE voltage limiter

they have a link on their web site that will walk you through the process of disabling the stock mechanical voltage limiter in the gas gauge. The info is in the Limiter FAQ section.

 

[Kevin74]

Google. RTE voltage limiter

they have a link on their web site that will walk you through the process of disabling the stock mechanical voltage limiter in the gas gauge. The info is in the Limiter FAQ section.

Yes sir. I found an awesome article with great pictures and instructions. Thanks for your help!

 

[RedFish]

There are 2 different methods. The first was published to a Imperial website many years ago. That is the method that RTE ran with and republished. The second was discovered by me and my brother about 12 years ago. the 2 methods cannot be mixed.
A typical 2 post gauge has only 1 current path through those 2 contacts. A 3 post gauge has 2 current paths through 4 contacts. The tape on the back isolates the gauge can from chassis ground. Then the switched 12 volts shouldn't go to the fuel gauge. it can, if you open the gauge and physically disable the limiter. I
In the more common instrument panels the 12 volts goes to the plug in type limiter, Not to the a gauge. So... 12 volts goes to the replacement regulator. Take it out of the round harness connector, add to its length if necessary, and route it directly to the regulator, no matter where you decide to place it. Now your 3 post fuel gauge will only function like any other 2 post gauge even if you dont open the gauge and disable that limiter.
I should add that if you dont go in and physically disable to OEM limiter, a volts meter would show 5 volts back feeding to where 12 volts once was. It can't go to ground through the housing. Electric tape stopped that. Without purchasing a nylon nut for that gauge stud, the 5 volts will go all the way to the contact pin where the 12 volt wire was. Thats where it ends. Its not a short, or a problem if there is no wire there.

 

[Kevin74]

There are 2 different methods. The first was published to a Imperial website many years ago. That is the method that RTE ran with and republished. The second was discovered by me and my brother about 12 years ago. the 2 methods cannot be mixed.
A typical 2 post gauge has only 1 current path through those 2 contacts. A 3 post gauge has 2 current paths through 4 contacts. The tape on the back isolates the gauge can from chassis ground. Then the switched 12 volts shouldn't go to the fuel gauge. it can, if you open the gauge and physically disable the limiter. I
In the more common instrument panels the 12 volts goes to the plug in type limiter, Not to the a gauge. So... 12 volts goes to the replacement regulator. Take it out of the round harness connector, add to its length if necessary, and route it directly to the regulator, no matter where you decide to place it. Now your 3 post fuel gauge will only function like any other 2 post gauge even if you dont open the gauge and disable that limiter.
I should add that if you dont go in and physically disable to OEM limiter, a volts meter would show 5 volts back feeding to where 12 volts once was. It can't go to ground through the housing. Electric tape stopped that. Without purchasing a nylon nut for that gauge stud, the 5 volts will go all the way to the contact pin where the 12 volt wire was. Thats where it ends. Its not a short, or a problem if there is no wire there.

Hi Redfish,
Yes, that makes sense to me now. Just don’t even send the 12V to the fuel gauge. Should be easier and less invasive than opening up the fuel gauge.

Thank you!

 

[RedFish]

Hi Redfish,
Yes, that makes sense to me now. Just don’t even send the 12V to the fuel gauge. Should be easier and less invasive than opening up the fuel gauge.
Thank you!

One advantage to opening the gauge is seeing the fuel gauge part of it fried as bad as the limiter side is. Then you send it to someone to be renewed. Pictures that websites use do not accurately depict what is more typical condition of a 50 year old fuel gauge.