Trying to get my gas gauge in my 49 chevy working. It was converted to 12v negative ground. it appears that a runtz was installed, I have 12v going in but nothing coming out, bad runtz I believe. I bought a resistor from classic. I think this would take the place of the runtz on the power post. I'm I correct? Does anyone have a wire schematic for the resistor? Does anyone have a photo of the resistor wired in?
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum
1. You don't say what the gauge is doing. You just say trying to "get the gauge working". 2. There are many issues that cause a gauge to "not work". It's not always the gauge. 3. A resistor just reduces the voltage to 6V.
Don't know what or how you tested the gauge but you say "12V going in and nothing coming out"......in and out of what? I will assume you know how to test for voltage. I will assume you tested the "Runtz" while it was hooked up to the gauge and the ignition was on. I will assume you realize that one side of "Runtz" will be approx.12V and the other will be approx. 6V. If you somehow are trying to test the gauge and are looking for an output voltage, there is none.
It's probably better to start a post with "my gas gauge is showing.........." What should I do?" Especially if you are not experienced. These gas gauge issues come up all the time. They are usually a ground issue. They can be a sender or a gauge issue also. They can be a power supply issue. They can be a broken wire issue. They can be an empty tank. Could be a "Runtz" ground issue.
As you can see by looking at the resistor you bought, it has a screw and nut on one end. That is where you attach your power wire with a ring tongue terminal on it's end. Screw them together. The other end is for the gauge power stud. A resistor has no polarity and it can be installed either end to either termination.
A Runtz is a solid state voltage regulator. Runtz is a brand name that we should not use because there are many brands and the name is protected. Anyway, this type is usually made using a TO-220 package ($1). It has three leads. It has good accuracy and built-in thermal overload protection. The three leads are: input, output and ground. The accuracy needed for our gas gauges is debatable. The thermal over load actually saving a gauge from damage, is debatable.
So anyone's choice: A $6 resistor or a $20 regulator.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
The above link to the PDF for Runtz instructions says that it is a "dash gauge voltage regulator" as Bartamos pointed out. It is not a dropping resistor. One Runtz regulator is used per gauge that requires voltage to operate. The ammeter is a current meter and does need one. Original AD truck water temperature and oil pressure gauges are mechanical. There have been postings of the Runtz failing and suggestions that they are caused by voltage surges when the starter solenoid is engaged. If this is true then, in my opinion, the Runtz needs to be redesigned to eliminate the affects of voltage surges.
A dropping resistor option can be used instead of the Runtz (connected the same way) but the voltage is not regulated so it may reduce the accuracy of gauge (more of a factor if the tank is empty but the gauge shows fuel remaining). Power resistors are typically used and they have a tolerance (resistance changes with temperature) of 5 percent. I have no idea of the best resistance value or the type resistor construction (carbon, ceramic etc) to use.
The best solution (my opinion) is to swap the gauge with one designed for 12 volts. It's not cheap and it requires (standing on your head) removal of the cluster and disassembling. The new gauge works with the same original 30 ohm fuel lever sensor.
Troubleshooting tips:
Runtz test: With the ignition switch off, remove the Runtz from the fuel gauge post. Connect your voltmeter positive lead to the Runtz connector that you just removed from the post. To be safe I like to tape this voltmeter connection. Connect the negative meter lead to a good ground point. Turn the ignition switch on. You should read 6 volts +/- a small percentage provided the 12 volt input from the battery is normal (edit: the output voltage can be higher depending on which regular chip is used in the design).
Gauge test: With the ignition switch off, remove the center wire from the gas tank sensor and tape it so that it doesn't touch ground. Turn the ignition switch on. The fuel gauge should read full. The center wire is not connected so this is maximum resistance as seen by the gauge. Also if the ground wire for the sensor is not making a good ground, it can have the same result as having an open wire or maximum resistance.
Fuel level sensor test: To fully check the fuel level sensor it needs to be carefully removed from the tank. First thing, disconnect the battery. You will have gasoline fumes so cover or tape over the tank opening. The sensor gasket will need replacing afterwards so have one available. Remove the ground and center wires from the level sensor. With your voltmeter switched to ohms connect one lead of the voltmeter to the center connector and the other to the metal base of the sensor. The fuel level sensor reads a very low to zero resistance when the arm is down (tank empty). With the arm raised to maximum, the resistance is 30 ohms +/- a small percentage. As the arm is raised and lowered, the resistance should change uniformly. If it is erratic or no change, the sensor is bad.
Last edited by buoymaker; 05/14/20212:47 PM.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
OK lets get this Runtz thing straight: This device will not be the source of a gauge problem. It's a great way to use your original gas gauge on 12V.
1. I believe it is a linear Voltage regulator with overload protection. A fuse would also protect the gauge further.
2. Assuming it is a linear Voltage regulator using a TO-220 package as I said, the whole advantage is that these can take any unsteady/unregulated voltage, in the case of a true Runtz, 8V to 28V and give steady output, in the case of Runtz...7.5V, Steady, as in: steady.
There is no voltage spike sent into the electrical system by the starter or solenoid.
3. I don't know the facts or knowledge behind anyone who says they "fail", "don't work", burn up or whatever.
4. The Runtz is used by many gauge rebuilders and sold by well known vendors. As I said, there are knock offs, there are people who call anything a "Runtz". I don't even know if someone like Speedway Auto, who sells Runtz, knows what they are saying. They use the word Runtz in quotations "Runtz". I'm afraid the word has morphed into meaning a reducer. The Chinese copies could be called Runtz by some companies not realizing it's a Brand name. Not sure. We all say Kleenex, Band Aid, Coke...those are Brand names that have become nouns.
5. A resistor will work, albeit not as accurate. The gauge can be protected by a simple inline fuse before or after the resistor. Wherever a person thinks is best.
6. The "Runtz Voltage Drop" was invented by the owner of Fifthave, Randy Rundle, with help from his friend Dan Schulz in 1992. They combined their names and got the word Runtz.
7. Randy passed away Feb 1, 2021.
TO 220. Not sure if he used this or not but I think that is what is under the shrink sleeving.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
Please don't shoot the messenger. The Fifthave PDF link above says (at Tech Tip), "This will protect your Runtz and any other solid -state accessories from damage caused by the voltage spike that occurs when the contact points inside of the starter solenoid are closed during engine cranking." My take is that Randy and Dan were/are aware of failures and they recommended to NOT use the wiring on the starter/solenoid terminal(s) as a 12 volt supply source but go directly to the battery.
I have read postings in the Fordbarn and Jalopyjournal where there are complaints of failures but they can't figure out why. Some members reply that they have never had a problem or failure.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
"I had first hand experience with early voltage regulators that would stick closed causing voltage spikes, so I wanted the Runtz to be "dead on" accurate and able to accept those voltage spikes without damage."
He is right and you were right to point it out. "Load Dump" is a factor. This can cause high voltage. I removed my comment. (strikethru). I should have done more research. Supposedly, there can be big spikes, I have not had this happen or know anyone who has on non solid state vehicles. As far as I know, the ground on the IC Randy used should redirect a large spike to ground to protect his IC. That is what I thought the ground wire is for. The device also has thermal overload protection and shuts down temporarily to protect the gauge.
Randy was a member here "Fifthave". Quite a prolific poster too. Here is the story about spikes from Randy.
Ok sorry for the vacation guys but i have been like the one armed paper hanger these past months....shop expansion and related....
As for the part time Runtz.... The Runtz has a built in circuit protection to protect the dash gauges from voltage spikes and shorts in wiring harnesses. If the Runtz detects a voltage spike it will shut down like a fuse until things cool down then will come back. It will do that about 4-5 times before it acts like a fuse and stops the flow of current completly.
This case sounds like enough of a voltage spike to just barely trip the Runtz.
That is why it is important to be sure the power to the ignition switch comes directly from the battery post of the battery and not from the amp gauge or starter solenoid as per original.
When the starter switch is closed to crank the engine a voltage spike is created that travels thru the electrical system ....about 300 volts worth. By powering the dash gauges thru the battery, the battery will "eat" those voltage spikes and protect the dash gauges from the voltage spikes.
This is important because the Runtz is a solid state device and is very accurate. If you notice most new positive battery cables already have a 10 gauge wire moulded into the battery clamp. That is what that wire is for.....to power the ignition.
All of this is also true for things like cell phones plugged into cigar lighters, and modern stereo radios... all need to have direct battery power.
Have you seen modern radios installed in old cars and soon after the LED lights are burned out and you cannot figure out what station they are on? A voltage spike is what took out the LED lights and soon ennough the radio itself will be next.
So the important lesson here is be sure the power to the ignition switch and any solid state accessories comes directly from the battery.... Class dismissed.... Randy
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
I have read postings in the Fordbarn and Jalopyjournal where there are complaints of failures but they can't figure out why. Some members reply that they have never had a problem or failure.
I've had two failures with the Runtz device. The first one likely failed because I wired it off the starter lug (worked for about two months). The second one failed even though it was wired from the battery(worked for about three months). No more Runtz devices for me........
I've read here on SB and on other sites about the use of a Zener Diode to reduce the voltage on a gas gauge. I've been using a 6.8V Zener Diode on my gas gauge successfully for about six years. This past winter in conversation with Jon G, I learned the Zener Diode needs to incorporate resistor(s) to limit the V so the Zener Diode doesn't overheat and fail. Attached is a 6.0V Zener Diode circuit diagram that includes two 3 ohm resistors. I still need to assemble these components to adequately protect my gas gauge.
Jon G, feel free to jump in here and set the record straight!
Interesting. Andy in both cases, what was the output voltage of the Runtz regulator after they failed? Did you buy them from the link mentioned above or somewhere else? Thanks.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
I believe they both had 12V input and no voltage on the output side as the gauge was not operable after the failures. I'm still using the same 6V gas gauge. Yes, they were purchased from the Fifth Avenue Internet Garage. I even spoke with Randy (may he RIP) about my experiences. He was most gracious to listen and offer his suggestions.
One more question Andy. Usually when a component burns/fails like the regulator chip, it emits a strange smell maybe something like melting wire insulation. Did you notice anything like that?
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
The zener diode is a good choice for something like this...and actually with a fuel gauge, you don't need an elephant gun to shoot a mouse. Just like Ohm's Law and other things electronic, explaining the zener can get complex, but here is a tutorial I think does a nice job of it:
Once established correctly a zener diode ought to last and work for a long time. And they're not expensive. I'll reserve comments about the other products out there, but honestly speaking...at least in my experience...the best, simplest and longest lasting (about 1 week past forever) 12 to 6 volt converter of all was the Vol-Ta-Drop. Unfortunately they stopped making them over 20 years ago. If you can find one, get it. Most people who still own one would be very hesitant to sell it.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
For about $10 (Amazon), you can buy a 12/24V DC to 5V DC converter. It would probably do the trick*. Just have to cut off the USB connector and add ring terminals.
*not sure how much current flows through a gas gauge.
2 amps or a bit less for the most hungry ones and some are only about a quarter of that. Once I have a bit of time, I'll see about making one (similar to what I did with the condenser replacement). This is a very simple thing which would only require a small bit of cost.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
Nice, easy to follow article on how to build them. Thanks Andy!
Not that I need one, but if I did (not being an electronics guy), sourcing parts on an individual basis, looked to be somewhat pricey. If you were to build ten you could build them cheap, but I couldn’t find decent pricing on individual pieces.
Last edited by Phak1; 05/16/20212:35 PM.
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum
Two things about the Runtz. * It's mounted on one end on the post of the gauge. If it has a circuit board, typical truck vibration could cause a small crack. Epoxy encasing may be needed. * If I was in the business, I would want the defective units returned to determine what component failed and revise the design.
Voltage surge. Operating a 6 volt, series wound (if I remember correctly) starter motor with 12 volts works but I don't know if this increases voltage surge. In any case, a protected auxiliary panel/box connected directly to the battery is probably a smart thing to do for providing power for all add-on solid state devices (today's tech electronics).
Power supply info (tech school stuff). * Dropping resistor = Poor regulation. * Resistor voltage divider = Basic regulation. Good regulation if input voltage is constant. * Zener diode = Good regulation. Correct resistor(s) and capacitor(s) have to be calculated. * 3 pin/leg regulator = Great regulation. Resistor(s) and capacitor(s) require no/minimal calculation. Built-in overvoltage, overcurrent and thermal protection.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
Rusty, I suppose we've completely hijacked this thread by most reasonable standards. However, there's a lot of really good information coming to the surface. Let us know if you want a new thread started on 12V to 6V regulators.
I thought I was grasping the Zener Diode with resistor(s) configuration, but the introduction of capacitor(s) has me scratching my head. Does the capacitor store excess voltage? I'm even more curious about the 3 pin/leg regulator with buoymaker's 'Great regulation' listing.
Could you resident electrical wizards (and you know who you are) walk us through these circuits from the battery to the gas gauge?
I don't pay much attention to my gas gauge until it stops jiggling from sloshing. When that occurs, I have 30 miles to get to a gas station. If I fail to notice when it stops jiggling and run out of gas, no worries. There soon will be a line of folks waiting in line to help me get back on the road. That is one of the perks of driving iconic trucks.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
Unfortunately we are going around in circles. I already gave the same info that was linked by Andy. It's not readily apparent however. I will try this approach. A linear voltage regulator can be purchased for $1-$1.5. The kind I'm speaking of comes in several "packages". The one I mentioned and supplied a pic is a TO-220 (Japan), they also come in TO-39 (Texas instruments) and TO-252 D-PAK (Motorola). These are just bodies and connection variances. All surface mount. The actual IC inside is made by various companies and packaged into the "body" with "permission". TO= Transistor Outline (package). D-PAK= DECAWAT PACKAGE.
The point is that Runtz is a 3 pin linear voltage regulator IC in a usable package. It was designed to be a DIY user friendly install. With all due respect, it was over designed. It is obsolete. This is a small issue with a giant blog. Of which I am participating in, due to Covid Lockup Syndrome. I have had both shots and still hiding from something or someone. I'm just following the voices in my head.
You can add capacitors for added accuracy/stability to the VR input and output pins. Not needed for our gas gauges. You can mount them on a pc board or rig them separate. You can add heat sinks, not necessary for the amp draw/wattage of our gas gauges. As I said before, these linear voltage regulators take a very unsteady higher input voltage and supply a very steady output voltage. These devices have built in thermal overload protection and short circuit current limiting. They are identified by letters (L , LM, etc. depending on manufacturer. National Semiconductor, Fairchild Electronics, etc.), then 78 and then the output voltage. KA7808 has a 8V output. All kinds of output voltages are available. XX7806 is 6V output.
A person wishing to build their own "Runtz" or VR can use any method they wish. As stated, wire them direct from battery. If I tried it, I would just solder wires directly to the three TO-220 pins and cover with heat shrink sleeving as the Hamb link shows. No heat sink. If I ever needed a reducer for a gas gauge, I would buy one from Classic Trucks for $6. Wire it direct from battery (just in case) and use an inline fuse to protect gauge. If the Runtz is wired direct, meaning no spikes, why is thermal overload protection and short circuit protection such a big sales feature? (Rhetorical)
Remember when getting all technical about this, that our gas gauge are inaccurate due to temperature variations. The gauge itself is a slow reacting, slosh dampening, needle to hash mark mismatched design to begin with. I'm like Carl, I don't look at it much or worry if it's not aircraft accurate. You will learn where empty is soon enough. Just get about 6V to it and be done. Lots of guys run them on 12V. Voltage drop keeps them going. So just run 14 feet of wire to them.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
Bartamos, I deleted my previous post and will not post more on this thread.
The picture was of Andy's defective original Runtz with the heat shrink removed. We are trying to figure out why it failed. Sorry if we got our wires crossed.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
And at the end of the day, it must be said the gauge is totally dependent on the sender. When I say totally, I mean that. I've found the AD fuel gauge to be as accurate as it needs to be. In fact, after testing 3 of them (from different years) some time ago I could not see any difference at all. I even resorted to making a paper scale with marks separated by 1/16" in an arc to better see any variations. But the senders? The original equipment senders were at best fair and honestly speaking they were designed to fail. They sold for about $7 at the dealership parts depts and they were meant to last about 5 years at the most. Of the senders available today there is only one of them I've seen worth even considering. It is sold by an eBay seller whose id is renbusan. Here is the 0-30 ohm sender he sells: https://www.ebay.com/itm/261122347319?hash=item3ccc1ad137:g:FBgAAOSwpPVgBuwZ&vxp=mtr
That sender isn't perfect, but it is pretty darn close to it. Why? Because it is a completely different design. It was designed and built in Taiwan by somebody who knew what they were doing. The wiping plane is flat, the sensing fingers are metal which connect to a special arc shaped poured-in-place resistance compound and the body is nylon. So the only thing that will wear out is the wiper button...and those typically last a good while. I've spent over 10 years studying fuel gauge senders off/on and the whole arena is quite challenging. I have designed and made one which is very close to ideal, however to make enough of them to sell will cost more than I'm prepared to spend at this time.
As I've posted here before, some of the senders I have seen are pure 100% junk. Take a look below. This was sold by a popular vendor I won't mention by name as a 0-30 ohm unit. It began life as a 0-90 ohm unit onto which the assembler dribbled hot solder until he/she had reduced resistance by 60 ohms. That is the sort of sending unit that makes people "think" their AD fuel gauge is bad.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
