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Instrument voltage limiter

Mark1972

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The instrument voltage limiter out of the back of the dash on my 1970 Plymouth Satellite. According to the wiring schematic, I should be getting 5v to the wire(dark blue) that leads to the fuel sending unit. I was getting 5v, but it was pulsing. From zero to 5 every half a second or so. Then after a few minutes nothing. Dead. I pulled this out and tested it. I put 12.3v into the 12v prong, grounded it to the car body, and tested the 5v prong. It put out 12.3v. It should have dropped to 5v I assume. Also, ohms are 60 from ground to 12v prong, 60 from 12v to 5v prong, and no continuity from ground to 12v. Even if the limiter is screwed and putting out 12v instead of the proper 5, should it not of showed 12v at the dark blue wire at the body plug? I just want to make sure this is the issue before I order a new one. As always, thanks again for the help. Hoping to finally hear it run by Sunday.

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Sounds like it's sort of working. I recently replaced mine with a rt-eng.com solid state unit. It has a heartbeat led and pulses electronically like the original electro mechanical. Great thing about these is the short circuit protection.
 
Had the same symptoms as yours I'd hear a ping the gauge would go to normal. Ordered a solid state one but before I put it in it stopped. Will change sometime.
 
They are supposed to "pulse" the voltage. What is actually happening is the +12 is pulsed to an "average" voltage of +5. In other words, the duty cycle of the pulsed +12 volts is such that for all intents and purposes it averages out to be about +5 volts delivered to the instruments.

As to the pulsing stopping, that is not normal. The bi-metal contacts are sticking open or closed depending on the output, nothing or constant +12.
 
The limiter will not pulse without a load. I used a 25 ohm resistor to simulate the sending unit.
Tim
 
The limiter will not pulse without a load. I used a 25 ohm resistor to simulate the sending unit.
Tim

If talking about the stock one actually that's not true. They work the same with 2 or 3 gauges, so if that statement was true the pulse will change, getting a voltage variation.

Points gets heated by chassis ground and voltage from RUN or ACC source ( depending on car ) enough to get the bimetally to heat and make it work without any load need, like turning and hazzard flahers need working in series with the bulbs, but they just drive positive. Then the output will be offering the pulse according with the heating element gap by the adjustement screw and speed taking to get heated and cooled.

Every limiter gets its own speed, no one is the same to the other one, but they are adjusted individually from factory according to that.

now if you talk about the RTE, can't tell if needs load, but doesn't sound logic to me
 
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They are supposed to "pulse" the voltage. What is actually happening is the +12 is pulsed to an "average" voltage of +5. In other words, the duty cycle of the pulsed +12 volts is such that for all intents and purposes it averages out to be about +5 volts delivered to the instruments.

As to the pulsing stopping, that is not normal. The bi-metal contacts are sticking open or closed depending on the output, nothing or constant +12.

Agree. There are videos on youtube of people testing them. Sounds like yours was working, but stopped. May be why you were having issues. I bought the RT-Eng one that was mentioned above for my instrument cluster when I went through it. Haven't installed it yet though, so I can't speak to how it works. They get good reviews though.
 
The rt-eng limiter will pulse without a load.
 
Another vote for the electronic replacement unit here. When I had my cluster out, I managed to repair damage to the pc board
and got all lights and gauges working on the bench with the electronic limiter.
In true redneck fashion, my 12V power source for testing consisted of a pair of jumper cables attached to my battery and the
other ends clamped to my wooden workbench. :thumbsup:
Yeah yeah, I know - but it worked and I didn't burn the garage down. :)
 
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I put an RTE limiter in my runner after burning a couple of gauges. Later in my valiant and a car I was working on I added limiters from Red line just because they did some work on them and the gas tanks read low. Turns out they are set at 4 volts so I made another call to RTE
 
I bought both the tach pcb with calibrator and limiter from rt-eng.com.
Great people. Big mopar guys and really sharp electrical engineers.
 
Well from what I learned reading responses, and from what I'm seeing with my current limiter, I ordered the solid state unit from RTE. As I mentioned, it was pulsing, which I now know is normal. But then stopped altogether. I gave it some light taps with a screwdriver handle, but nothing. Hopefully the new unit takes care of the issues I'm having. Thanks again for the help.
 
Once again, false.

No need load to get the pulse. The limiter works by itself. Is DIFFERENT than the blinkers flasher which requires load.

Points will open and close as far gets the ground via Chassis and the 12 volts input, no need for more. That's all what it needs to heat the bimetallic with the heat caused by the short on coil around like a resistor, feeded by the mentioned sources: chassis ground and the 12 volts input.

If load was needed the limiter would change the output being installed on different clusters between 2 or 3 gauges! Like when a turning light is blown and the flasher goes usually faster.

When misses the chassis ground ( for whichever reason ) when you turn the key on, points will remain closed sending full 12 volts. Since there is not a short, there is no heat to open the circuit. This will burn the gauges unable to hold 12 volts.

The output can be checked with an analog tester or test light. Of course that won't get you the voltage reading but just that the limiter is pulsing so then in working order. And any of those devices add any load
 
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