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Does anyone have personal experience with a gauge conversion from six volts to 12 volts? I'm aware of resisters being available but my question is about converting the gauge itself to 12 volts. There are tons of companies who advertise but I'm looking for someone who's actually had experience with having it done and can provide first hand feedback. Thanks.

On an AD truck, the only gauge to change would be the fuel gauge. I've seen where someone modified a 12 volt donor used-gauge, that was compatible with the original 30 ohm fuel tank level sensor and put an AD decal on it. It worked well and looked original. The thing is you have to contort your body to get up underneath the dash and remove the cluster. But first you have to remove all the other gauge connections and be extra careful with that copper capillary-tube water-temperature sensor that you don't crack or crimp it during removal. You have to remove the chrome bezel around the cluster assembly and not break the glass. Once you have been through that ordeal with added choice words to boot, you will not want to mess around with a modified gauge hoping that it works and continues to work okay. Buy a new gauge that is already made for 12 volts and 30 ohms. This is one situation where if you cheap-out, you may regret it later.

I bought a 50 1/2 ton that had a half a 12 volt conversion job. I corrected the mistakes and bought and installed a new fuel gauge. No resistors or voltage converter needed. Worked well and fuel level sensing was as accurate as original. The guy I bought saw what I did and wanted it back.

The best voltage reducer ever made is the Vol-Ta-Drop, but the company went out of business years ago. If there was more demand, I'd make those today and sell them. It used a simple coil of resistance wire to drop the voltage. Accurate and fail-proof. If you ever see a working one on eBay or elsewhere, it wouldn't be a bad idea to buy it. I have one I got nearly 50 years ago when they sold for $7. It will still be working when dinosaurs return to the earth as long as nobody monkeys with it. I imagine somebody is going to show up and suggest you use the Runtz gizmo. I'm not a fan of that one at all. Converting the gauge itself won't be nearly as easy as you might hope it would be. If this is your hope, you'd be better off making a fuel gauge out of an early 70s pickup fit the AD cluster and swap your 0-30 ohm sender for a 0-90 ohm sender. I may actually have one of those fuel gauges at home. Will look to see if you want when I return. Just send a PM if interested.

I put a Runtz on it today and it's dead. 12.8v at the input and 0v at the gauge. They said send it back and they'll replace it but most of what I'm reading is that they are crap. If you decide to make some in the next couple of days I'll buy one.

Hey guys! The man said, "I'm aware of resisters being available but my question is about converting the gauge itself to 12 volts."
That pretty much negates add-on coils, resistors, 3-pin regulators and voltage dropping devices.

I bought a 12v gas gauge from Classic Parts. Tough to put in, as you need to remove and open the gauge cluster. It works good and I have had no issues with it since.

That makes two of us.

Tiny, I have converted gauges, 6V to 12v. Converted Ammeter to volt meter. It depends what year, the gauge and so on. Basically you keep the face and bezel and replace the meter movement from a new 12V gauge. PM me with what you have. The Runtz or Runtz style or resistor does work.

I put a Runtz on it and it's DOA. Doing some research on the Runtz (of course after I bought and installed one) I discovered they have a high failure rate out of the box. It seems any conversion of the actual gauge would be a challenge. I did, some years ago, own a 55.1 panel that I converted to 12v. It never occurred to me that I might need to protect the gas gauge and I put over 100K on the truck after the conversion with the gas gauge working fine the whole time. Since I now have a much harder time crawling under the dash than I did in 1970 and having read tales of woe from folks who say they've destroyed their gas gauge on 12v, I'm being a bit more cautious about possibly killing mine. I think what I'll do is put a buck converter on the gas gauge, similar to the one I put on the heater motor. They are inexpensive and easy to install. The one on the heater seems to be working great. The one I put on the heater is good up to 10 amps output and the one I ordered for the gas gauge is 2.5 amps which should be more than adequate. Buck converter

Sorry the runtz failed but not surprised. I have a feeling the runtz has become the new Chinese ignition condenser. I'll give this subject some thought when I return home. There are several voltage reducers being sold on eBay and all of them appear to be the same design or a slight variation of it. It does appear to be a valid electronic scheme. If it is working on your heater fan, that is encouraging. The one criticism I had was it might not dissipate heat well enough, but the heater fan uses much more juice than the fuel gauge. Years ago VW decided to continue to use 6v fuel gauges in their 12v Beetles, although not many people knew it. Cost savings? You can decide...they used a voltage reducer similar to a common voltage regulator in the automotive generator circuit. We used to joke about them. Truth was they could have had the coils wound for 12v for a fraction of the cost of that vibrator device.

Well. since the forum wants to talk about Runtz, I'll bring this up. Some swear by the Runtz and some don't. Some get upset if you post negative against it. HandyAndy had two Runtz (absolutely not a clone) to fail. He was kind enough to send me one so I could investigate. In this order left to right in the picture. Capacitor, Diode, 3-pin Regulator and Capacitor. The design of the circuit is basic, not copyrighted and is used as an example in one of the manufacturer's spec sheets. The regulator chip had failed. The other components were good.

The 3-pin regulator is a Fairchild KA808R in a D-Pak configuration. All of the components are surface mount devices (basically, no leads). There is no heat sink for heat dissipation of the regulator chip. The circuit board had no evidence of burning or a burning smell of a component that had failed. Specs says the KA808R output is good for up to 1 amp at less than 15 watts. The circuit board was enclosed in a heat shrink tube (not watertight).

Four things that bugged me. One is, no heat sink (it can get hot inside an AD cab). Two, the Runtz is mounted on a threaded stud of the cluster gauge assembly. What would happen if the cowl vent was opened and you happened to come up on a rain storm? Would it fail if it got a little wet? Three, is 1 amp - 15 watts enough? Testing is required. And finally four, why use a 8 volt regulator when the system is 6 volts? The voltage drop across a diode is typically 0.6 volts.

Let the cat fight begin.

I bought my gauges from Bowtie Bits years ago.. already converted to 12 Volts.

Not sure about the cost anymore but D&M Restorations in Greenville S.C. has did several gauge projects for me over the years and they are still working to this day. Never one lick of problems and a couple are over 20 years, a couple of them just 5 years.
I'm just lucky they are only about 30 miles from my house.....

I've joined in posts when members wanted to ask about Runtz. Examined how they are built and helped explain how they work and so on. That was because folks wanted to discuss Runtz. It's all in the search function.
Now we are discussing how they fail and all kinds of ways of reducing 12V to 6V. Worrying about the heat.
I try very hard to answer the question and stay with the poster.

Tiny, you specifically asked how to convert a gauge without using a resistor/reducer. You said you knew all about those components.
I did answer the question. You didn't want a reducer, you didn't want to buy a converted gauge, it seemed you wanted to know if others had converted their own.
Then you changed to saying you tried a Runtz, it failed and we are off to the races again.
Buoymaker said "Hey Guys".,,,,,,,trying to say what I'm saying now. Then he gave up and joined the crowd. If you have decided to use a reducer, and this goes for everyone else on these questions, why don't folks buy the $6 one from Classic Trucks? I would really like to know. This is a low tech issue. There is no worry about heat whatsoever. Everyone knows resistors create heat. Like the one on heater switches. If a rheostat is used, that is just a variable resistor. The one Classic sells for higher loads than a gas gauge has a heat sink.

Can we please stop talking about Runtz units and all the other clones. If the "reducer" at Classic trucks does not work, please advise. If it does work, buy it. Why would anyone want to build one for a gas gauge? The Classic one is probably an axial lead resistor, the others are solid state. Whatever. The Runtz style accuracy and built-in thermal overload is not needed. Spike protection is provide by direct wiring from battery and a fuse. Too much technical talk about a gas gauge.

Bart, I don't understand. I mentioned the Runtz only in response to your post immediately above mine. You said they work, I said I tried one and it failed. Initially I did want a converted gauge because I didn't see a suitable alternative to the Runtz type resistor. I then thought about the buck converter I used on my heater and how one would probably work on the gas gauge so I mentioned that. Further consideration led me to think that using a buck would allow future restoration to stock if my son desires. How is that upsetting?

Tiny, you and I are friends. Don't want to injure that. Probably a mis interpretation by us both. As far as I can tell, you tried a Runtz before I posted. You did repeat that statement later on after I posted.

Regarding my statement, I see what you mean. Here is what I said:

"The Runtz or Runtz style or resistor does work".

I was trying to say that voltage reducers work. Any type a person wants to use. I was not saying that you can't get a bad one. The "resistor" method works and has worked for a 100 years. I don't know about the reliability of a Runtz brand. I don't know if the Classic one has good reliability. That's why I asked. But the concept works, that is what I meant. I got confused when we switched from converting a gauge...... to using a reducer so fast. Not upset. Just pointed that out. It was a major shift in the post in my view. Abandoning the convert question and then we concentrated on the Runtz brand and not the concept. Other types of reducers and etc. Whether a Runtz brand reducer is good or not, has been covered before. All manner of DIY and reducers have been covered before.
I was trying to explain that shift; and trying to separate several issues within the post. Not aimed at anyone. I understand you wanted to avoid the reducers because of bad vibes. The best remedy is not converting a gas gauge, it's using a reducer. Unless otherwise specified, I recommend the Classic Parts $6 job. Sorry for any remarks that seemed like disrespect.

I'll take the blame for mentioning the runtz thing. Honestly I brought it up because anytime somebody says they're interested in going from 12 volts to 6 volts, the runtz gets suggested and then a lot of people seem to step up and encourage the idea. In simple terms it isn't what I'd say is the best option. The failure rate for a product like that should be 1 in maybe 100,000 or 1 in 1,000,000...and it seems to me it is much greater.

What impresses me is simplicity, durability and as close as possible...a zero failure ratio. Same reason I would never suggest anybody purchase the Pertronix. Have you noticed? With the Pertronix failure is expected almost as much as if you had Charlie Manson pack your parachute.

When I get home, I'll study this and see if I can come up with another answer.

Jon, you are not to blame for anything. There is no blame to give anyone.

In my opinion, the Runtz should be super reliable. It uses a purchased potted device used in aircraft, space, etc. They add a PC board for connection and solder it and sleeve it.
If the component is a National semiconductor or Texas Instrument or other well known maker, it should be super reliable. Many of these companies buy from China. Their parts would be spec certified and tested at production and retested at incoming.

The Runtz component could be a substandard non certified part. Those are available for non flight safety type, non critical type consumer products and cheaper priced. Now that Randy Runtz has passed away, I wonder if the family business is aware of the negative reputation that may be building and what they have to say. There are many complaints on the internet. There are possible other reasons: Electrostatic Discharge damage. EMF damage. If there really is a high failure rate, It can be anything from postal scanners to static in the air to Chinese dumping to low quantity buyers. Then of course user error. At any rate, it's easy to avoid this device. I feel sorry for the Family. It doesn't look like anyone is on top of this. Offering to replace with another bad part will actually kill the company faster. The only thing going for them is it's a household word for old vehicle conversions. Like Kleenex is to facial tissue, like coke is to beverage, like Jacuzzi is to hot tub..... The Runtz is a solid state voltage regulator. It must be properly grounded. This will provide ESD protection and is necessary for operation. The metal tab with a hole in it is a heat sink. The ground is a black wire.

I don't know if any of this applies but it's in our tip Section.

Also this is important Click

What you and I and a few others here understand, Bart is anytime you "sacrifice" (for lack of a better word) 6 volts from 12 volts, it isn't as though you went to the grocer and selected 6 potatoes out of a display of 12 and just innocently purchased those. The 6 missing volts must basically be destroyed continuously whenever the circuit is made and that creates heat. Heat to many electronic components is instantly or rapidly fatal---depending almost entirely on the rating/quality of the component, how rapidly that heat builds up and how effectively it can be dissipated. In cases of poorly made discrete components or an incorrect application, the damage can be almost a guarantee...and that is what I expect is the root problem here. The runtz device (from my observation) seemed to have more than expected failures right from the start. Two years ago a neighbor reached out to me, complaining the ignition control module in his Ford had failed and kept failing no matter how many of them he installed. Turned out Ford had used an incorrect heat transfer material between the module and the heat sink. It formed a ridge of about 1.5mm, the newly designed module sat atop that ridge and unless you worked with acetone to remove that, the module could not dissipate heat fast enough to keep from burning itself out. As I said I'll give this some thought. Anyone who knows me already knows I would never connect my name to anything expected to fail. Look at the "alternate condenser." Months of study went into that...the selection of the capacitor, the German maker's corporate philosophy and history, the design and then after that several were sent to people to test and see if there were any reasons they didn't work so changes could be made. I imagine if (and I doubt I'll be around long enough) I sold 1000 of them that there would never be a single failure. It isn't something designed to be changed when points are changed and it was also designed to help keep points alive longer. I've mentioned the Vol-Ta-Drop. That was a very clever product. A single coil of special resistance wire divided into 2 lengths and put into a ceramic box. That's all it was. One length of the coil supplied voltage for the radio and the other length to other accessories. The company is gone now but back when I talked to them there had been no failures at all. They made the product for both 12 and 24 volts and converted into 6, 8 or 12 volts.

As I mentioned, simplicity, durability and a zero failure rate...and I don't see that in the Chinese condenser, the runtz device and some other things out there.

Our tip section needs attention, by the way.

Please let me point out something. The circuit board is professionally-made and uses surface mount components. A small business is not likely to have the equipment to make these. It is common practice for a engineer/designer to come up with a design on paper, make experimental models to "stress test" then farm out the final design to a company that has the capability to mass produce. During assembly, things can go wrong. Parts can be cracked, overheated and mispositioned for example. The parts purchased by the assembler may have defects. Now back to the small business. The first batch may work well and last a long time. Then a new batch made fails in a few months. This is when the tough part begins digging through what went wrong. Not unlike Takata Airbags. With the tragic personal loss, the small company may not be able to investigate...I really don't know. Also, these units are sold at low cost and probably little profit.

If you look at the picture of unit that failed unit, I don't seen anything obvious that looks damaged. The output of the regulator is not zero volts but a very low voltage which could mean one or more of the internal circuits of the chip have failed. These are my observations and opinions. What would help is for everyone that has a unit to fail, do a little checking and take pictures before throwing them in the trashcan. I would think the regulator chip can be removed and hand wire a new chip with a small heat sink. See what happens next.