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Discussion Starter · #1 ·
A few years back when we rewired the car we made two solid state / electronic instrument cluster voltage regulators. Both are twins made from Radio Shack components. The setup was working perfectly until earlier tonight when I removed the cluster.

After reinstalling everything, I went for a test drive. Well now the temp and fuel gauge do not work. I returned to the garage and pulled the cluster again. The ICVR was hot.

I tried the extra one we made as a spare. It gets hot with just they key on and car not running. Gauges still do not function. With the key on I get 12v on input side and fluctuation between 160-170mv and 1-2v on the output side. It heats up in only a few seconds.

I'm guessing something is grounding when it shouldn't? Anyone have thoughts here? This is the early Falcon style.
 

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You may have transposed one side of the ICVR and the cluster ground. I saw that done once and it made one of the turn signal bulbs light constantly and no gauges work. That's a recipe for a fire ! ! If that didn't figure it out, take the battery cable off until you do.
 

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Discussion Starter · #3 ·
I did have wonky turn signals, but have LEDS from GTOnavy including his special single turn signal led with a ground wire that grounds to the screw on the back of the ICVR. I think that wire wasn't grounded good though. That issue seems to fixed now.

I had thought about having those two wires reversed but they have opposite connectors which makes that hard to do.

With the gauges disconnected the output voltage is 5v. Makes me think something is wrong with a gauge or wiring to them. It is all relatively new with no hacked up wiring.
 

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Discussion Starter · #4 · (Edited)
Having the temperature gauge connected seems to cause the regulator to heat up. With it disconnected the fuel gauge works and the regulator stays cool.

I checked both gauges for resistance across the terminals and they are both 12.9 ohms. Thought maybe there was a problem with the temp gauge itself. Doesn't seem so.

I can't find any damaged wiring from the gauges.
 

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Discussion Starter · #5 ·
Seems the culprit just showed it's ugly face. One of the studs on the back of the temperature gauge is loose or broken.
 

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Seems the culprit just showed it's ugly face. One of the studs on the back of the temperature gauge is loose or broken.
I was going to ask about a short in a gauge or possibly an oil or temp sender on the engine, maybe a burned and grounded wire across the intake or something. I hope that's it...
 

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Discussion Starter · #7 ·
I think the gauge post was grounding against the cluster housing. The opening is very close to the mounting stud terminals. I'm wondering if the funky nuts didn't hold it secure and it dropped down making contact.
 

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This is actually a good subject and question....

Do most people leave in and just use their Original ICVR.....or did you replace yours...and if so, With What??? and How long has it been running????!??

VERY CURIOUS TO SEE THE RESPONSES!!!

:eek:)

Tony K.
 

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Plus one...
I am considering solid state conversions but we no longer have Radio Shack and I don't know what components to get.
 

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Every time I think I am getting to get the hang of cars someone comes along with a question like this and I realize that I really don't know anything. I know what the individual words mean, but I don't understand what they mean together and why it would be used... Is anyone willing to explain what a solid-state electronic voltage regulator for instrument clusters does and why you would want one?
 

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ICVR = Instrument Cluster Voltage Regulator.........Greek Translation.


There is a small Voltage Regulator on the Back of the Instrument Clusters of all Classic Mustangs....

:eek:)

Tony K.
 

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To expand on Tony's definition, the gauges run on 5-6v, while the rest of the car operates at 12v (minus the coil). So there's the small voltage regulator on the back of the instrument cluster to drop the 12v down to 6ish for the gauges.

The originals are mechanical devices with moving parts in them kinda like the turn signal relay. There's a piece of metal laying between the two electrical connectors. Electricity flows through it and it gets hot and bends breaking the connection. Then it cools off and straightens back out and makes the connection again. This repeats many times per second and overall the voltage will average about 6v with it going between 0 and 12v constantly.

The modern solid state ones have some capacitors and a voltage regulator chip in them to put out a constant voltage with no moving parts.

Either way works. I've still got the original in my car but you can see the appeal of having a constant voltage without an old metal tab moving back and forth a dozen times a second or whatever it does.
 

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To expand on Tony's definition, the gauges run on 5-6v, while the rest of the car operates at 12v (minus the coil). So there's the small voltage regulator on the back of the instrument cluster to drop the 12v down to 6ish for the gauges.

The originals are mechanical devices with moving parts in them kinda like the turn signal relay. There's a piece of metal laying between the two electrical connectors. Electricity flows through it and it gets hot and bends breaking the connection. Then it cools off and straightens back out and makes the connection again. This repeats many times per second and overall the voltage will average about 6v with it going between 0 and 12v constantly.

The modern solid state ones have some capacitors and a voltage regulator chip in them to put out a constant voltage with no moving parts.

Either way works. I've still got the original in my car but you can see the appeal of having a constant voltage without an old metal tab moving back and forth a dozen times a second or whatever it does.
Thanks Magnus. It sounds like you are describing a buck converter (solid state) or a linear regulator (mechanical). Is that right or is there more to it?

I didn't realize that the original gauges use 5-6v. Thank you for that.
 

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I didn't realize that the original gauges use 5-6v.

This is what I was taught. If the gauges were wired directly into the cars 12V electrical system the voltage to them could vary anywhere from 12.5V (a fully charged battery) to 14.5V (an alternator's maximum output). So the gauges' accuracy could vary significantly in that 2V range of difference. A small voltage regulator was added to the gauge circuit to keep the voltage at a constant level regardless of the voltage in the car's electrical system. Obviously the gauge voltage has to be below the car's average voltage. The engineers could have just as easily chosen 8V or 9V instead of 6V. I'm no EE so maybe there is a good reason why they chose 6V for the gauges.
 

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Lots of vehicles besides the classic Mustangs and not just Fords operate on 5-6 volts for the gauges. I still have the originals in all 3 of my cars and considered switching to solid State for the same reasons we do for the voltage regulators under the hood...reliability. I have noticed some times on old cars where they either peg out at max briefly or don't work at all because they "stick"... all things with moving parts eventually wear out.
 

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Discussion Starter · #17 ·
Made a successful 200 mile round trip yesterday. It was the gauge post grounding out on the cluster housing. Wondering now if there is an insulator missing.
 
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