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**Guest** · May 13, 2012, 02:28 PM

Hey Kevin,
Borrowed this form another post (Thanks to Ray) "Checking voltage to the input side of the CVR unit should show a steady 12V reading. Checking the voltage out of the other side of the unit to the gauges should show a fluctuating reading, with the average reading being about 6V. But it will probably be fluctuating back and forth. If it is, your CVR unit should be good. If you have 0V or 12V on the output side, your CVR unit is probably bad. Not only that, it might have fried your gauges also.

Richard D. Hord

**YellowRose** · May 13, 2012, 05:43 PM

Constant Voltage Regulator

Kevin, from what you have said about getting about 4v on the output side of the CVR should indicate that you have the proper voltage coming out of it. Usually that is a fluctuating voltage between 0-5 or 6v. I see you have grounded the CVR unit. Check and make sure you have a good ground connection. Check to see that you have the wiring coming from the output side of the CVR unit plugged into the correct connector on the fuel gauge on the back. Then make sure that you have that fluctuating 0-5 or 6V coming out of the back of the fuel gauge and going to the Temperature gauge so that gauge has the power it needs.

If the wiring is right, your gauges should be working, but perhaps need adjusting. Unless, sometime in the past, there has been a problem with a CVR unit. IF a CVR unit went bad, and passed through a continual 12V output to the gauges, it could have burnt the wiring between the input side of the gauge, and the gauge itself. That wiring is pretty thin and it is my understanding from what I have been told, can burn pretty easily if subjected to a constant 12V. The gauges are 6V gauges and that is why Ford used a Constant Voltage Regulator to step down the voltage from 12V to a fluctuating 0-5 or 6V. In talking with the techs at the Bird Nest, they tell me that what usually happens to the gauges is a failure of the CVR unit, allowing 12V to go down the wires to the gauges, burning out the wiring and possibly damaging the gauges. Or at least breaking the connection between the input connection and the gauge. What they have done in the past is take heavier duty wiring from a Flairbird and replace that thin wiring with it.

Since you are getting 4-5V output to your gauges, and if you think you have the wiring connected correctly, try making the adjustments to the readings that are outlined in the Technical Resource Library (TRL) which is always part of my signature element. Click on that link, scroll down to the section regarding the CVR unit and look for the information on adjusting the gauge readings by turning the star wheels on the back. It might just be a matter of adjusting the readings to fix the problem.

If that does not fix them, and you suspect the gauges might be shot, the Bird Nest does a great job of repairing them. They did mine, and they also quartzed my clock for me. You can find their contact information in the Advertisements Forum. They really know their stuff.

I just noticed something you said. You said "My CVR has a good 12v going into it. When the ignition is turned to on it registers 12v, then drops to 0 v and then alternates between 0v and about 4v. Ive tested two of these and the other one alternates between 0v and about 6v." I was assuming that you were talking about the OUTPUT side, but I am not sure now. IF that is the reading you are getting on the INPUT side to the CVR unit, then that is a problem! From the ignition switch, you should be seeing a steady 12V input to the CVR unit. If it is fluctuating between 0V-6V, you must be looking at the OUTPUT side. If you are sure you are looking at the INPUT side it should not be fluctuating but a steady 12V reading...

If anyone else has any thoughts on this, please post.

**kevin_tbird** · May 17, 2012, 01:34 PM

Thanks for the replies. I have a steady 12v input. Output goes to 12v and then fluctuates between 0-4 or 0-6v output. I've tried (electrically) adjusting the fuel gauge using the instructions in the service manual , but could not get it to reach all the way to full.

All wiring is new. I was uncertain if the output should fluctuate between 0-12v or 0-5v. The TRL writeup was not clear for me on that point. If it was 0-12v with an average of 5 then I had a problem. If it was 0-6 volt with an average of 3.x then the CVR is fine. I still am not 100% clear.

Kevin

**YellowRose** · May 17, 2012, 02:37 PM

Constant Voltage Regulator

Hi Kevin, I don't think that CVR unit should be outputting 12v and then quickly drop to a fluctuating average of 5v. I would think that you should be seeing a fluctuating 5v on the output side of the CVR and not 12v at all. I am wondering if that is just momentary reading and then it drops immediately to 5v. Someone might want to comment further about you seeing 12v out of the output side. I am going to post an article that explains how the CVR works. It has four pages. It also says that you should be seeing a fluctuating average of 5v.

http://www.squarebirds.org/SB/Fuel-T...20Wiring-1.jpg

http://www.squarebirds.org/SB/Fuel-T...20Wiring-2.jpg

http://www.squarebirds.org/SB/Fuel-T...20Wiring-3.jpg

http://www.squarebirds.org/SB/Fuel-T...20Wiring-4.jpg

Clicking on each image should enlarge it so you can read it better. Hopefully, this will help you understand what the CVR does and how it works. Also, and I do not know if this is true or not, but a mechanic told me that when you have the ignition turn on and the gauges indicating, do not expect the fuel gauge pointer to be on the E when the tank is empty or on the F when it is full. Instead it should be sitting on the lowest mark for Empty and the highest mark for Full, not the letters. The same thing applies to the Temperature gauge I think. However, I do not know how factual this is. As for adjusting the readings on the gauges, try to set them at the lowest point you can for Empty or Cold, and the highest point you can get it for Full or Hot. If you can do that, then you will have some readings that you can trust hopefully. I hope this helps.

**kevin_tbird** · May 17, 2012, 02:57 PM

I spoke with the electrical guy at the birds nest (great guy) and he gave me some trouble shooting tips. The best one was to use a 12v test light to check the CVR instead of the gauge. If it flashes your getting 12v. Sure enough it flashes. I guess the analog gauge just cant capture the peak voltage. So my CVR is good

I then grounded the negative side of the gauge and tapped 12v on it until it reached the peak. I was performing the role of the CVR. That worked too.

Then I attached the CVR output to the gauge and the fuel gauge does not go to the peak when I ground the gauge. It gets about 3/4 of the way. The temp gauge will get to peak.

At this point I am assuming I must have some type of wiring problem and I'll need to diagnose.

After messing with the wiring I started the car and the ignition switch will not turn it off! I'm getting power past the switch somehow. Guess I'll need to climb underneath an look at what wires I moved.

Kevin

**simplyconnected** · May 17, 2012, 11:56 PM

Originally posted by kevin_tbird

...I then grounded the negative side of the gauge and tapped 12v on it until it reached the peak. I was performing the role of the CVR. That worked too.

Then I attached the CVR output to the gauge and the fuel gauge does not go to the peak when I ground the gauge. It gets about 3/4 of the way...

The CVR has no way to drop voltage so it gives an AVERAGE of six volts by being on half the time. New solid state CVR's actually output constant six volts (and are much more accurate).

When you were 'tapping' with 12-V, apparently you were way over 50% duty cycle which caused the gauge needle to peak.
But, when you went back to the OEM CVR, it only went to 3/4 because the CVR may be averaging 40% duty cycle.

Originally posted by kevin_tbird

...After messing with the wiring I started the car and the ignition switch will not turn it off! I'm getting power past the switch somehow. Guess I'll need to climb underneath an look at what wires I moved...

Just refer back to the pictures you took before you tore into it, Kev. The Key Switch (S) only gets one wire and so does (B).

Don't get the two Black and Green wires mixed. One goes to IGN and the other goes to ACC. They DO NOT go together. Hope this helps. - Dave

**kevin_tbird** · May 18, 2012, 06:25 PM

Pictures. Oh yah those pictures. Actually I didn't take pictures or take anything apart. A little diagnoses indicated that the starter relay was stuck open. New relay so I'm not sure why, but a quick tap took care of it.

Back to the CVR. After diagnosing operation and wiring with the gent from the Birds Nest we determined the CVR was switching on the wrong cycle. Adjusted the CVR and the gauges are now working fine.

Well. Almost. Turns out when the body of the CVR is grounded to the dash (per wiring instructions and the way it is suppose to work according to Birds Nest) the gauges don't work Keep the body ungrounded and they work fine. Ideas are appreciated, right now I am cutting out isolating gaskets.

Kevin

**simplyconnected** · May 18, 2012, 11:59 PM

Originally posted by kevin_tbird

...A little diagnoses indicated that the starter relay was stuck open. New relay so I'm not sure why, but a quick tap took care of it.

I'm sure you mean it was stuck closed. I wonder why the starter motor wasn't constantly engaged, but ok.

Originally posted by kevin_tbird

...we determined the CVR was switching on the wrong cycle. Adjusted the CVR and the gauges are now working fine.

Well. Almost. Turns out when the body of the CVR is grounded to the dash (per wiring instructions and the way it is suppose to work according to Birds Nest) the gauges don't work...

Huh? Switching on the wrong cycle? LOL, no. The CVR needs a good ground to be consistant. If it gives longer duty cycle ungrounded, get a new one, ASAP.

Ray swears by the solid state types so I support that suggestion as well. In a nutshell, do not circumvent the root problem by going around it. Fix the root cause, and quit making insulators.

**YellowRose** · May 19, 2012, 02:27 AM

Constant Voltage Regulator

Kevin, I do not know what is going on with your CVR, but as was said, the instructions say it must be grounded to work properly. I went through three OEM style CVR's before I found the Real Time Engineering solid state version and installed it. I have not had a gauge problem since then. I am told that the OEM style CVR's available today are often found to be made in China and as such are also known to fail. After blowing about $75 on OEM style CVR's, 3 years ago I invested in a $50 RT-Engineering IVR3 unit (NOT the IVR4. It is not for our cars). It has been working ever since. Here is some information on the solid state IVR3 right from their website. BTW, you will not find Ford listed as one of the makes this unit works on, but it does. I never got around to telling them that.

"Real Time Engineering has a new solid state limiter that will replace the original mechanical limiter on the back of your dash. This new limiter has many advantages over the original limiter, and also has advantages over the linear regulators that hobbyist have been using as well. The biggest advantage is that our limiter doesn't have a mechanical set of points and a heater wire that can break and fry your gauges (which is what the original mechanical limiter had).

Our limiter exactly duplicates the original limiters function by slowly switching 12V on and off. Our limiter has a built in polyfuse which protects the limiter and your wiring from short circuits on the output of the limiter. Our limiter constantly looks for short circuits on the output of the limiter and will switch itself off if a short circuit is detected. When the short is removed, then the limiter starts working again. Our limiter has a built in diagnostic LED that blinks when the limiter is on, helping you see that you have power to your dash and that the limiter is operating properly. Our limiter has a warm up time at turn on, same as the original mechanical limiter. This means that your gauges will come up to the proper reading very quickly. Our limiter is always outputting a constant 5V average, no matter what the input voltage is (Within the range of 9V to 18V). If the input voltage goes too high or too low, then the limiter shuts off."

Click on the Technical Resource Library (TRL) in my signature element below and you will find the link to RT-Engineering where you can order an IVR3 unit. Save yourself the headache of troubleshooting and fixing present and future gauge problems and get a IVR3. There is a link to the Installation Manual for the IVR3 you can click on and read or print out. It mentions a condenser and three wires, but we only have the 12V input and the 5V output to be concerned with. BTW, when I took out my instrument panel, mine was NOT attached to the back of the panel. It was mounted/grounded to a metal support bar behind the instrument panel. Someone probably had problems with the CVR unit in the past and mounted it there.

**kevin_tbird** · May 19, 2012, 06:30 AM

Before I go to the IVR3 I'd like to get the stock style working. This car has everything stock, right down to the correct style screws that you cannot see.

Simply connected: I'm not trying to bypass the problem I'm trying to diagnose it. Working with the electrical guy from the Birds Nest seemed to be the best way. I'm glad for your help.

The duty cycle we are talking is adjustable on the stock style CVRs. The average voltage was below 5v on two differ CVRs when bench tested (using a 12v bulb as a load and analog gauge. Increasing the duty cycle got us to about 5.5v average. The other way tjo check was that the test light would come on only about 30% of the time, not 50%. Of the two CVRs one was in the vehicle for at least the last 40 years and one was brand new.

I've checked resistance on each sensor feed wire. Great continuity and no resistance for both of them. Neither was shorted to ground.

The gauges both work on the bench using the gauge itself as the load and tapping a 12v source on and off with the sensor wires connected to ground.

With the CVR in the vehicle ( frame not grounded ) the gauges work fine - registering correct values. When I grounded the CVR body with a jumper wire the fuel gauge slowly dropped to near zero and the temp gauge went their immediately ( yes I was running the car at the time to check the accuracy of the temp gauge.

So instead of throwing parts at the problem (it may come to that) lets try and figure out why a ground at the CVR frame is necessary and why it would make a difference to the gauge output. I'm glad to build a bench setup if we can come up with a good idea on how to test.

Thanks
Kevin

**Joe Johnston** · May 19, 2012, 11:35 AM

I'm gettin' more confuseder than ever since reading these posts along with my +6V ground vrs 12- ground post and the links mentioned therein.

1) I understand the importance of good grounds but fail to see how they are any more important than good corrosion free hot wire connections. As I see it the only difference is the ground is in our old non plastic component cars is part of the structrue of the component. Would a component work better with 3 power leads to it, and if so how reduntant can we become in establishing grounds? Does each component need a separate ground wire like new vehicles with all the plastic components? If multiple grounds are so essential, lets make the cars from copper like the wiring, wouldn't that be better? (understand I mean in theory not economically).

2) I see frequent mention of the CVR being 6V and 5V here and other places. My old Little T-Birds nedded no CVR and I know they were 6V or 12V guages depending on the year of the vehicle and the incompatability of mixing 55 & 56 components in the dash.

3) I see mentioned some CVR's not working with "our cars". Is that because they put out an average of 6V instead of 5V? If so, that means Ford changed from their original 6V guages, then to 12V guages and then to 5V guages while having 5V guages in Thunderbirds and 6V guages in their other cars and trucks at the same time. Econoomics doesn't support that, or does it and I don't comprehend.

4) Mentioned in the other post was the fact that economics came into play as well as standardization to make the decision to have a - ground system. Having a 5V in a Thunderbird and 6V guages in cars and trucks at the same time for nearly identical parts certainly doesn't seem to be economical.

At the beginning of one of the links posted the phrase "Opening a can of worms" was stated. Someone straighten me out because I see a lot of contridiction in the info and am confused over something that should be rather cut and dried.

**YellowRose** · May 19, 2012, 12:46 PM

Constant Voltage Regulator

Sorry for any confusion I might have caused regarding 5v-6v CVR's. The gauges in our Squarebirds (and other Tbird models after that, I think) were 6v gauges. That required the use of the Constant Voltage Regulator to drop the 12v in these cars to something between 5v-6v. I often used 6v as the figure, but the articles written about the CVR use 5v. It is my understanding the the CVR internal system drops that 12v to something that the 6v gauges can handle, averaging 5-6v using a 50% duty cycle if I have this right. As Dave said, new solid state CVR devices, give you a steady 6v output. I don't know if this is gonna clear things up or not. Maybe Dave can, if I didn't.

**Jimz Bird** · May 19, 2012, 01:40 PM

Well, let's see if I can confuse it more.

This is just Baby Bird stuff but I "think" it will apply from the 57 up which has the CVR.

55 is of course 6V and no CVR needed. You can use a 6V "Lantern" battery to check the gauge and it should go to full. If you measure the resistance across the terminals it will measure 11-12 ohms.

56 is a 12V gauge and while it looks the same as a 55, it isn't and won't work in a 55. It is a 12 volt gauge but the resistance across the terminals is 38-40 ohms so it is "internally" voltage reduced to function like a 6V gauge. This was the only year the Tbird has a 12V gauge. Again, no CVR needed.

The 56 passenger car gauge is also 12V and is similar to the 57 style Tbird but won't work in the 57 because - here we go - 57 started using the CVR and the gauge in the 57 is a 6V with a resistance reading of 13-14 ohms. The 57 CVR reduces the 12V to 6V.

The CVR is at times referred to as an "Instrument Voltage Drop Regulator" or a "pulsating voltage drop bi-metallic power regulator".

A caution from the 55-57 Restoration Manual when checking the CVR:
"The "pulsating voltage drop bi-metallic power regulator" provides reduced voltage (max 9V) to the fuel and temperature gauges. CAUTION, this unit must be installed and grounded with mount screws prior to operation check or applying voltage. If power is applied without a ground the unit sends 12V to the fuel and temperature gauges causing both gauges to fail."

Now we have from 5-9V. Probably the resistance in the sending units ties in to this somehow.

Once again @Dave D et al. for clarification.

There ya go Joe, clear as mud?

**simplyconnected** · May 19, 2012, 04:04 PM

You're on the money as usual, Jim. 1956 (Ford, Lincoln, Mercury, & Trucks) is the ONLY year for 12-V gauges. (I didn't believe this at first, until the Master Parts Cat's proved it.)

It's all about 'duty cycle' (the 'on' time vs the 'off' time). Battery wires and starter motors are grossly undersized but they are only on for seconds, then off for many minuites.

Back then, Ford could not use a simple current dropping resistor because the currents change from "F" to "E" and from "C" to "H". Both gauges are in parallel, so 'constant voltage' was easier to achieve by using slow gauge movements and an average voltage.

Ford also used a bi-metal strip with a contact in your gas tank sending unit. So, a cycling voltage source was connected in series with a gauge and a gas tank unit that used current to cycle, causing your gauge reading. Cold days would initially show less gas than hot days.

So, CVR cycles need to be very regular. That's why it needs a solid ground. Full 12-Volts is applied to the gauges, but only for half the time. The 1955 T-bird system is 100% duty cycle at six volts, which is exactly the same power without a CVR. - Dave

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