Voltage limiter

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66Glassback

66Glassback

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I have a 1966 Barracuda with a bad fuel, temperature and oil pressure gauge. I did some research and found that the voltage limiter is in the fuel gauge and it is supposed to bring down the voltage to 5 volts for all three gauges. I am getting a steady 12 volts at the temp sensor and the fuel sending wire. According to the service manual I should be getting fluctuating voltage that will average out to be around 5 volts. There is a way to disable the 12 volt feed to the fuel gauge and install an external voltage limiter. Could anyone walk me through that procedure? I saw pictures but I am not sure what is being done. Especially in the fuel gauge disabling the 12 volt feed. Thank you.
 
The voltage limiter feeds the fuel and the temp gauge. It's only a matter if it is attached to either first. I believe 64 is fuel and the temp later 65/66 limiter feeds temp first and then fuel. Regardless your (I assume light) oil gauge is separate. I rebuilt a 64 cluster with an electronic limiter. Works well.
 
The voltage limiter on a 1966 Barracuda is in the fuel gauge. the 12 volt feed comes into the fuel gauge, is reduced to 5 volts then goes to the temp gauge and the oil pressure gauge. It doesn't have an external limiter. I am looking to put an external limiter on my cluster to replace the one that doesn't work.
 
66Valiant528 said:
The voltage limiter feeds the fuel and the temp gauge. It's only a matter if it is attached to either first. I believe 64 is fuel and the temp later 65/66 limiter feeds temp first and then fuel. Regardless your (I assume light) oil gauge is separate. I rebuilt a 64 cluster with an electronic limiter. Works well.
Click to expand...
This is not a good way to put this. There is no "first," or whatever. They are all three in parallel. The article posted is what you want EXCEPT not necessarily the home built limiter. You can buy a solid state one from RTE and adapt that.

RTE as example

RTE limiter - rte

www.rt-eng.com www.rt-eng.com

Another article about converting the internal gauge

RTE Gauge Faq - rte

www.rt-eng.com www.rt-eng.com

Here is how they work. The fuel gauge has three terminals. One is 12v INTO the gauge UNIT and that 12V supplies power TO the internal limiter. It feeds the regulated voltage (5v + / - ) to the fuel gauge, and ALSO outputs the 5V to the second of the 3 studs. That stud then jumpers the 5V over TO the other two gauges, oil and temp. The 3rd stud on the fuel gauge, of course, is for the fuel sender.

User Redfish has written a lot about these writing cautions to avoid screwing up the gauge, which of course is delicate. One method is to CAREFULLY separate the old limiter contacts and gooping it with "Goop" (that is the name) or RTV to keep the contacts apart. If you can, it might be good to isolate the 12V stud from the limiter, or remove/ cut the limiter heater so it cannot fail/ short and cause problems

I recommend you rig some sort of test resistors, so that you can test the system END TO END. They all use the same resistances. Feed 12V and ground to the cluster, hook a test resistor from one gauge sender to ground, and the appropriate resistor should give the correct reading. Here is an old photo of a brand X test box showing the resistances

c-3826-jpg.jpg


Generally, be sure the senders are grounded, and not overtightened. Suspect problems in the bulkhead connector for temp and oil. Fuel goes through the rear harness. Add a dedicated ground pigtail to the cluster and ground it to the dash/ column support. Take the nuts on the gauges and loosen/ tighten them 3-4 times to "scrub" them and make good connections.
 
Pardon my poor wording. I installed an RTE limiter. The 12v feed goes to either the fuel or temp gauge depending on year make and model and then drops the voltage from the internal VR and then feeds the other gauges. Again depending on year make and model. Sorry if that wasn't clear. The 'first" is the 12v feed.

20240609_091618.jpg


20240609_091641.jpg
 
67Dart273 said:
This is not a good way to put this. There is no "first," or whatever. They are all three in parallel. The article posted is what you want EXCEPT not necessarily the home built limiter. You can buy a solid state one from RTE and adapt that.

RTE as example

[/URL]

Another article about converting the internal gauge

[/URL]

Here is how they work. The fuel gauge has three terminals. One is 12v INTO the gauge UNIT and that 12V supplies power TO the internal limiter. It feeds the regulated voltage (5v + / - ) to the fuel gauge, and ALSO outputs the 5V to the second of the 3 studs. That stud then jumpers the 5V over TO the other two gauges, oil and temp. The 3rd stud on the fuel gauge, of course, is for the fuel sender.

User Redfish has written a lot about these writing cautions to avoid screwing up the gauge, which of course is delicate. One method is to CAREFULLY separate the old limiter contacts and gooping it with "Goop" (that is the name) or RTV to keep the contacts apart. If you can, it might be good to isolate the 12V stud from the limiter, or remove/ cut the limiter heater so it cannot fail/ short and cause problems

I recommend you rig some sort of test resistors, so that you can test the system END TO END. They all use the same resistances. Feed 12V and ground to the cluster, hook a test resistor from one gauge sender to ground, and the appropriate resistor should give the correct reading. Here is an old photo of a brand X test box showing the resistances

View attachment 1716260313

Generally, be sure the senders are grounded, and not overtightened. Suspect problems in the bulkhead connector for temp and oil. Fuel goes through the rear harness. Add a dedicated ground pigtail to the cluster and ground it to the dash/ column support. Take the nuts on the gauges and loosen/ tighten them 3-4 times to "scrub" them and make good connections.
Click to expand...
 
67Dart273 said:
This is not a good way to put this. There is no "first," or whatever. They are all three in parallel. The article posted is what you want EXCEPT not necessarily the home built limiter. You can buy a solid state one from RTE and adapt that.

RTE as example

[/URL]

Another article about converting the internal gauge

[/URL]

Here is how they work. The fuel gauge has three terminals. One is 12v INTO the gauge UNIT and that 12V supplies power TO the internal limiter. It feeds the regulated voltage (5v + / - ) to the fuel gauge, and ALSO outputs the 5V to the second of the 3 studs. That stud then jumpers the 5V over TO the other two gauges, oil and temp. The 3rd stud on the fuel gauge, of course, is for the fuel sender.

User Redfish has written a lot about these writing cautions to avoid screwing up the gauge, which of course is delicate. One method is to CAREFULLY separate the old limiter contacts and gooping it with "Goop" (that is the name) or RTV to keep the contacts apart. If you can, it might be good to isolate the 12V stud from the limiter, or remove/ cut the limiter heater so it cannot fail/ short and cause problems

I recommend you rig some sort of test resistors, so that you can test the system END TO END. They all use the same resistances. Feed 12V and ground to the cluster, hook a test resistor from one gauge sender to ground, and the appropriate resistor should give the correct reading. Here is an old photo of a brand X test box showing the resistances

View attachment 1716260313

Generally, be sure the senders are grounded, and not overtightened. Suspect problems in the bulkhead connector for temp and oil. Fuel goes through the rear harness. Add a dedicated ground pigtail to the cluster and ground it to the dash/ column support. Take the nuts on the gauges and loosen/ tighten them 3-4 times to "scrub" them and make good connections.
Click to expand...
Thank you for all the information. I am going to purchase the IVR3 and try it. Hopefully my gauges are still ok.
 
You can test your gauges by connecting 1.5 volt batteries to them. 3 batteries equals 4.5v so you can "test" the gauges with approximately VR voltage. 1 battery =s about a 1/3. 2 about 2/3 and so on. Good luck.
 
I did the exact same mod on my '66 Barracuda except that I didn't take the fuel gauge apart (as in pulling the face plate) but instead, I drilled a hole in the gauge housing to get access to sterilizing the voltage limiter. I posted some photos here somewhere a couple of years ago. Test to see if your gauges are still good first. If the fuel gauge is bad, you can use it to experiment on.
 
I used a $10 generic 5 VDC adjustable DC-DC converter from Amazon or ebay in my early-A's (voltage limiter inside fuel gage). Looked just like a Mopar-specific one that was sold on ebay for $35. The adjustment helps you tweak the fuel gage to read correctly at full or zero. To tweak both limits to correct, I had to add ~20 ohm resistors in parallel with the sender. There are mechanical zero and scale adjusters on the gages, which is via bending tabs, but intended only as a one-time factory calibration. Re temperature, if the gage holds steady while driving, that needle position would be the T-stat setpoint (usually 180 or 195 F), since it is controlling. I wouldn't get too hung up on whether that sits exactly at midpoint on the gage.
 
I just got my new IVR3 limiter today. I was wondering, instead of disabling the ground or opening up the fuel gauge if I could just remove the G1 wire from the plug going to the Cricut board? It is the voltage limiter and the fuel gage feed wire. Then use this wire to power up the new limiter and then supply the 5 volts out of the limiter to the third post on the fuel gauge?
 
I have concerns about testing the gauges with 3 batteries in series. Testing I have done using 5VDC power supply has the gauge at FS (full scale) with 1.3 V at sensor, so 3.7 V would be across the gauge. I don’t know what would happen with 4.5 V across the gauge, but unfortunately, I don’t have a gauge I want to sacrifice for the sake of experimental collateral damage!

The RTE device outputs a square wave 10 V P-P (peak-peak). At 180, the reading was too low and not adjustable. However, my mods require a DC gauge power, so I will use an adjustable unit so the readings can be set to a better position.
 
FYI, Correction on the RTE testing

The initial results were using a very light load of 120 ohms. Upon further testing, as the loading increased below 100 ohms and down to 10 ohms, the waveform changed. Also, the peak voltage was influenced by the applied voltage where it decreased as the voltage was changed from 13.8V to 10.8V.
 
I tried a 1.5 V battery just to verify the temp gauge worked at all. It went to about 1/3 so 2 batteries it went to like 2/3rds. Good enough. It works.
 
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