Converting a 6V dash cluster to 12V

[AllenV]

Hey All,
I have a 55 F100 with a nearly original interior. I am correcting the sins of the previous owner and trying to make a basic, mostly original truck. This is a very specific question that needs a separate post and heading. I have a long term post here:
https://www.fordbarn.com/forum/showt...ghlight=allenv

The truck has been converted to 12V negative ground, I want to keep it that way. The original instrument panel has been abandoned in favor of a set of “Pep Boys” little round gauges attached to the bottom lip of the dash. These are fuel, oil press, water temp, battery volts. I want to remove the after market items and reinvigorate the original dash instruments. As far as I understand the original instruments run off of 6V and that I can install a constant voltage regulator to down convert the 12V supply to the dash to 5V. ( I am looking at a Mustang part here: https://www.cjponyparts.com/scott-dr...1968/p/HW2881/ )

The ammeter ought to work fine. The tricky bit is the other sensors. Do I have to install vintage oil pressure and water temp and fuel level sensors? Certainly the oil sensor must change as the aftermarket rig has a little plastic pipe feeding pressure the back of the aftermarket gauge while the ford panel wants an electrical input. FYI, the motor is a 292 Y-block circa 1959.

Who has done this? How did you do it? Will a 5V regulator succeed? I believe these trucks were originally positive ground. Do I need to adapt the dash to a negative ground? Please offer myself and the others the benefit of your experience.

[Dobie Gillis]

"The ammeter ought to work fine. The tricky bit is the other sensors. Do I have to install vintage oil pressure and water temp and fuel level sensors?"

The ammeter will work on 12v. You need to reverse the direction the feed wire passes through the loop on the back or it will indicate backward. Also, the pointer swing is less on 12v due to the lower amperage. I would use vintage senders for the fuel, temp and oil pressure if you can find them. Modern senders won't work with the original gauges since the originals operate on a different principle from modern ones. There are some suppliers who have senders they claim are compatible with the original gauges, Dennis Carpenter being one of them. The other alternative to achieve your goal is to convert the gauges to be compatible with modern senders. Several instrument repair suppliers can do this but it's pretty spendy.

[dmsfrr]

Originally Posted by AllenV

Hey All,
I have a 55 F100 with a nearly original interior. I am correcting the sins of the previous owner and trying to make a basic, mostly original truck. ...

The truck has been converted to 12V negative ground, I want to keep it that way. The original instrument panel has been abandoned in favor of a set of “Pep Boys” little round gauges attached to the bottom lip of the dash. These are fuel, oil press, water temp, battery volts. I want to remove the after market items and reinvigorate the original dash instruments. As far as I understand the original instruments run off of 6V and that I can install a constant voltage regulator to down convert the 12V supply to the dash to 5V. ( I am looking at a Mustang part here: https://www.cjponyparts.com/scott-dr...1968/p/HW2881/ )

The tricky bit is the other sensors. "Do I have to install vintage oil pressure and water temp and fuel level sensors? Certainly the oil sensor must change as the aftermarket rig has a little plastic pipe feeding pressure the back of the aftermarket gauge while the ford panel wants an electrical input. FYI, the motor is a 292 Y-block circa 1959.

Who has done this? How did you do it? Will a 5V regulator succeed? I believe these trucks were originally positive ground. Do I need to adapt the dash to a negative ground? Please offer myself and the others the benefit of your experience.

Originally Posted by Dobie Gillis

... I would use vintage senders for the fuel, temp and oil pressure if you can find them. Modern senders won't work with the original gauges since the originals operate on a different principle from modern ones. ...

I have a 12v converted '55 that I'm still working on.
Yes the original '55 gauges need original '55 senders to function correctly.

I'm totally unfamiliar with a '55 truck dashboard, can you attach a photo?
Does the original dash have a gauge for oil pressure or an idiot light? An actual voltage gauge or a red 'Gen' light?

The smaller '57+ Temp sensor in the '59 head can be replaced with the larger '55 Temp sensor, to match the original gauge by drilling & re-theading the bushing in the head. (been there, done that)

An original fuel tank sender should work with an original Fuel gauge.
Because they function with bi-metal switching contacts (not variable resistance) allowing current flow & creating heat in the gauge the original Fuel & Temp gauges should not be voltage or polarity sensitive. No voltage reducer needed.
Depending on the style of the gauge faces it may be possible to purchase original style 'new/replacement' gauge & sender matched pairs made to function on 12v.

Here's a link for some background info. It was written for '55 TBirds but most of it applies to '55 Fords in general.
https://www.ctci.org/battery-for-6v-to-12v-conversion/

"Do I need to adapt the dash to a negative ground" Nothing to do here unless there is an original '55 radio or clock in the dash. It won't hurt to double-check the polarity of the ignition coil.
.

[Sanddoc]

Most instrument clusters actually use 5v. and have a voltage regualator behind the
dash... Don't ask my why... on my 62 Ford and 74 Dart I made an electrontic
VR very easy... just a resistor... use the same case..

I often wonder why the need for 5v and not use 12v, but then I was always
interested in positive ground ... not so much the 12v vs 6v. as the 6v starter has
more torque... but as lights and accessory change. 12v became norm, now it's going to 24v...

[miker98038]

This is an old but accurate post about how the King Seeley gauges work. It doesn't address the voltage change, but you might find it helpful if you need to trouble shoot things down the line.

http://forums.y-blocksforever.com/Topic22135-1.aspx

[AllenV]

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Thank you for the excellent replies so far. I'll dig into those links and other info this evening. Here I post an image of the dash. You'll see idiot lights for oil and current. I suppose that might be the most difficult configuration to make work.

[AllenV]

Originally Posted by Sanddoc

Most instrument clusters actually use 5v. and have a voltage regualator behind the
dash... Don't ask my why... on my 62 Ford and 74 Dart I made an electrontic
VR very easy... just a resistor... use the same case..

I often wonder why the need for 5v and not use 12v, but then I was always
interested in positive ground ... not so much the 12v vs 6v. as the 6v starter has
more torque... but as lights and accessory change. 12v became norm, now it's going to 24v...

I am willing to assume that Ford was just cutting cost by using low-voltage instruments for many years after they made all cars 12V. As far as resistors for down conversion...I am an electrical engineer and using a resistor for this job is inefficient and only works at the single current draw for the resistor was selected. If the current draw of the dash changes from that "design" value the voltage delivered to the dash electronics will be altered. I was happy to find that Ford put a proper voltage converter in Mustangs and that I can buy one as reasonable cost (linked above).

[Dobie Gillis]

Actually they adopted 12v instruments with the '56 models. That only lasted 1 year and they went back to 6v instruments for '57 (with a gauge resistor) on up until some time in the '80s, I think. The '56 12v instruments must have been problematic otherwise they would have kept them.

[hotrodart]

[QUOTE=. The '56 12v instruments must have been problematic otherwise they would have kept them.[/QUOTE]




I had zero issues with my '56 Victoria gauges in the 10+ years I drove it.

[Dobie Gillis]

Understand, but there must have been something that prompted them to revert to 6v.

[dmsfrr]

Originally Posted by Dobie Gillis

Understand, but there must have been something that prompted them to revert to 6v.

In '57 Ford began using re-designed circuitry using variable resistance instead of bi-metal switching contacts creating heat which operated the gauges.

Fyi, the original dash gauge voltage regulators were not a resistor but a bi-metal switching / chopper type device that created an 'average' lower voltage output.

The old style gauge & senders are generally self-regulating and don't usually need voltage reducers. A side effect of the older senders is they created switching static in the electrical system and needed radio suppression capacitors, the silver cylinder on a black wire in the first photo. They were not needed with a resistance type sender. (photo two)

[Dobie Gillis]

OK, forgive my ignorance but couldn't they have used 12v with the variable resistance gauges? Why did the gauges revert to 6v with a voltage reducer beginning in '57? Inquiring minds want to know...

[dmsfrr]

Originally Posted by Dobie Gillis

OK, forgive my ignorance but couldn't they have used 12v with the variable resistance gauges? Why did the gauges revert to 6v with a voltage reducer beginning in '57? Inquiring minds want to know...

I don't know either.
There was likely a reason based on cost effectiveness of the parts in question, multiplied by the tens / hundreds of thousands of cars & trucks built.
Probably based on some electro-mechanical functions and formulas I'm not at all familiar with.
.

[Dobie Gillis]

The mystery deepens. I'm sure there were records of the reasoning and decisions. Unfortunately some of that was lost to a fire in the archives section of the Rotunda in 1962. We may never know.

[AllenV]

This is fascinating. I had no idea how the engineers of the time solved these challenges. My EE education dates to about 1980, when transistors were fully matured and electromechanics was old-school. Anyway, I found some further info over at FordTruckEnthusiasts. The attached image is for a 60’s ford. It pulls together much of what dmsfrr has been offering and adds detail of the senders and the voltage regulator. What I am learning is that in the 60s and earlier, before transistors were economical and the all-electronic alternative would have been vacuum tubes, the 12V supply from the alternator-regulator combo was not well controlled. Without further voltage stabilization the instruments would have variable readings caused by voltage supply fluctuations. The clever bi-metallic switch instrument voltage regulator used the thermal time constant of the heating caused by the 12V input to build a switching 5V power supply. The effect was to isolate the instrument panel from the 12V supply variation. No doubt the inductance of the gauges and resistance of the sensors would have smoothed out the switch pulses.

[Dobie Gillis]

Makes sense...I think. The '56 gauges with no buffer must have been jumpy which caused enough customer complaints that they fixed it by going back to 6v gauges with the regulator to smooth the gauges out.

[dmsfrr]

I'm not aware of the '55 or '56 gauges being jumpy.
It could have been the newer resistance style senders were enough less expensive to make, even adding the cost of the regulator.
.

[Dobie Gillis]

Maybe. I don't think we'll ever know for sure. The power supply back then was a generator with a mechanical regulator. They were pretty "noisy" what with the regulator contacts making and breaking. I hate unsolved mysteries...

[AllenV]

I'd like to thank you guys for this discussion. I've learned some new things about the car "ticks".

I have decided to defer this instrument project for quite a while. I have much more important fish to fry with Nellie ( the truck). It seems that tackling instruments now would severely complicate the prime goal of getting healthy and driving.

[5851a]

I once converted a 52 F series and used the gauges from mid/late 70's P series trucks. They looked the same and bolted right in used the IVR and they worked. I left the gas tank sender up to the owner as he was using a large tank on the frame of the F-6. The older bimetallic IVR's sometimes had a little "Choke" added on them that I assumed was for radio interference. Good luck with your project. I didn't use the P series amp gauge because the original worked fine.