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Old 05-21-2019, 04:53 PM   #1
drolston
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Default Runtz Failures

The scene in the photo below was with 1/4 tank on the fuel gauge, which has been very accurate in the four years since I converted to 12 volts, using three Runtz voltage reducers on Fuel, Oil pressure, and Temperature.

When I filled the tank, the fuel needle went completely out of sight on the high end. Ignition off, it the needle settles at just below the empty mark. I replaced the Runtz on the fuel gauge with a spare, and the needle still went off scale high. I tested the removed part and all three installed Runtz and found all four to be putting out 8 volts.

With 8 volts on the oil pressure gauge and the engine off the oil pressure reads 10 psi. That is a big problem. When first converted to 12 volts, the oil pressure gauge matched the mechanical gauge.

So, in four years of light use all four Runtz failed in the same mode, namely putting out 8 volts instead of 6. Very odd. Just glad they did not fail to 12 volts; all of the gauges survived the voltage failure.

I have an spare CPT voltage reducer rated at 7 amps for the wiper motor and heater fan. It bench tests at 6.1 volts. I will report back after that is installed. I will be interested to see the effect of correct voltage on engine temperature indication, as that has been reading hot. Wishful thinking!
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Old 05-21-2019, 06:49 PM   #2
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Default Re: Runtz Failures

You can get 7805 in 5-volt or 7806 in 6-volt and fabricate an IC type CVR. You might try testing your gauges with a 6-volt lantern battery or what have you. At least you can test the gauge.

The old 6-volt systems made 7.1 to as high as 7.5 volts to charge the battery. 8-volts is a bit high but may offer a bit more amperage. The amperage is cut back quite a bit on some.

Where did your IC chip type VRs come from? Randy Rundle should have some sort of warranty on his units within reason. Others, I don't know. They have to be properly set up in fabrication to work but they are generally pretty reliable as long as the polarity is never compromised.

Last edited by rotorwrench; 05-22-2019 at 12:46 PM.
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Old 05-21-2019, 07:08 PM   #3
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Default Re: Runtz Failures

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Originally Posted by rotorwrench View Post
You can get 7805 in 5-volt or 7806 in 6-volt and fabricate an IC type CVR. You might try testing you gauges with a 6-volt lantern battery or what have you. At least you can test the gauge.

The old 6-volt systems made 7.1 to as high as 7.5 volts to charge the battery. 8-volts is a bit high but may offer a bit more amperage. The amperage is cut back quite a bit on some.

Where did your IC chip type VRs come from? Randy Rundle should have some sort of warranty on his units within reason. Others, I don't know. They have to be properly set up in fabrication to work but they are generally pretty reliable as long as the polarity is never compromised.
I got my Runtz voltage reducers from Speedway in June 2014. They worked fine until recently. They have not been subjected to reverse polarity. Or any voltage spikes that I know of. It is just weird that all four are now putting out 8 volts!

Maybe someone would stick a voltmeter on an installed Runtz output (the flat piece that bolts to the instrument) with the ignition on, but engine not running.
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Old 05-22-2019, 02:37 AM   #4
51 MERC-CT
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Default Re: Runtz Failures

Could never understand the wisdom of putting a 'Runtz' or any other reducer on each gauge when a single reducer would take care of the whole gauge cluster.
The same way Ford did it when they went to 12 volt systems and kept their 6 volt gauges.
The same type as used on '64-'65 Mustangs and which I have been using for over 20 years with no issues.
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Old 05-22-2019, 02:59 AM   #5
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Default Re: Runtz Failures

I junked my Runtz yrs ago and went with a gauge guy in Idaho who made his own volt drops using diodes.He claims that the orig Ford gauges are truly a 5V,not 6.Never ever had a problem since and always accurate.He is now retired.
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Old 05-22-2019, 04:03 AM   #6
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Default Re: Runtz Failures

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The KS gauges arenīt to sensitive to voltage at all.
Less voltage they just works slower...anything between 5-8v should work just fine.
But if the regulator canīt deliver the current needed they start acting funny...
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Old 05-22-2019, 08:29 AM   #7
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Default Re: Runtz Failures

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Originally Posted by 51 MERC-CT View Post
Could never understand the wisdom of putting a 'Runtz' or any other reducer on each gauge when a single reducer would take care of the whole gauge cluster.
The same way Ford did it when they went to 12 volt systems and kept their 6 volt gauges.
The same type as used on '64-'65 Mustangs and which I have been using for over 20 years with no issues.
I agree. I have used the Ford drop for many years. Started using it after the failure of some Runtz volt drops.
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Old 05-22-2019, 10:19 AM   #8
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Default Re: Runtz Failures

Made my own 12V to 6V reducers using these instructions. Cheap, easy to build and they have been working flawlessly for the past 20 years. I mounted mine right on the back of the gauge cluster.

http://www.studebaker-info.org/Tech/6-12V/6-12-6.html
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Old 05-22-2019, 01:10 PM   #9
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Default Re: Runtz Failures

Some folks use the heat sinks like that and some don't. The ones made by sources other than Randy Rundle may be suspect. If they are all showing 8-volts then they may be 7808 VRs. They make them in about every voltage you can imagine. A lot of electrical guys recommend the 5-volt 7805 type CVRs but I don't know if it will make a big difference. The KS instuments will take whatever current that they draw at any given reading. The lower voltage will keep the heat down in the units. I think that's why Randy Rundle recommended to use just one Runtz per instrument. The more you draw the hotter it will get.

Many of the repop instrument voltage regulator replacements have a 7800 series IC VR inside. The original ones were chopper types. They work the same way the gauge does on King Seeley systems. They have a heater coil around a bi-metallic strip with a little set of breaker points to regulate the voltage. If you put an old d'arsonval type volt meter on them, the voltage reads all over the place because it's constantly opening and closing the points. With a solid state CVR the voltage is "constant" as it should be.

There may be other problems brewing in the system like a loose terminal or something of that nature causing the instruments to read funky. That's why I suggested a test with a 6-volt battery. If nothing else, a person can see if it changes the readings.
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Old 05-22-2019, 02:28 PM   #10
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Default Re: Runtz Failures

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Originally Posted by 51 MERC-CT View Post
Could never understand the wisdom of putting a 'Runtz' or any other reducer on each gauge when a single reducer would take care of the whole gauge cluster.
The same way Ford did it when they went to 12 volt systems and kept their 6 volt gauges.
The same type as used on '64-'65 Mustangs and which I have been using for over 20 years with no issues.
In principle, I agree, and I ran one I got from NAPA for several years. But being a repro (no old Fords in the boneyards around here), it could not maintain anywhere near a stable voltage. I could watch all the gauges swing back and forth about 2 needles' width as the CVR cycled. I bought an electronic unit adequate for all 3 gauges (not Runtz), and have nice stable readings. The price was also similar to the CVR.
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Old 05-22-2019, 04:18 PM   #11
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Default Re: Runtz Failures

How do you check one of the Ford CVR units to see if it is working properly? Can you use a multimeter?
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Old 05-23-2019, 10:19 AM   #12
drolston
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Default Re: Runtz Failures

So, replaced all three Runtz that were putting out 8 volts with a single voltage reducer that puts out 6.1 volts. Much to my chagrin, the problem is not fixed. Oil pressure reads about 10 psi with the engine off and Temp sits at 1/4 deflection with the engine cold. Fuel gauge went almost out of sight high with a full tank.

What would cause all three instruments to read high? Anybody else ever have this problem?

First rule of electricity: " If something is acting weird, check the ground path." Seems most unlikely, but I will check instrument panel ground.

Did I mention how much I hate working under the dash?
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Old 05-23-2019, 12:27 PM   #13
51 MERC-CT
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Default Re: Runtz Failures

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Originally Posted by drolston View Post
So, replaced all three Runtz that were putting out 8 volts with a single voltage reducer that puts out 6.1 volts. Much to my chagrin, the problem is not fixed. Oil pressure reads about 10 psi with the engine off and Temp sits at 1/4 deflection with the engine cold. Fuel gauge went almost out of sight high with a full tank.

What would cause all three instruments to read high? Anybody else ever have this problem?

First rule of electricity: " If something is acting weird, check the ground path." Seems most unlikely, but I will check instrument panel ground.

Did I mention how much I hate working under the dash?
Don't know what CVR unit you are using but the Ford type units should have the outer case grounded. And the male spade fitting is the plus side (positive)
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Old 05-23-2019, 12:31 PM   #14
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Default Re: Runtz Failures

What sending units are you using, originals or repro?
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Old 05-23-2019, 12:43 PM   #15
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Default Re: Runtz Failures

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What sending units are you using, originals or repro?
All original gauges. Original tank sender. Repo temp and oil pressure senders. All worked fine, until recently.
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Old 05-23-2019, 01:14 PM   #16
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Default Re: Runtz Failures

None of the reproduction senders hold a candle to the OEM King Seeley units but a person has to find either good used or old NOS stuff.

On the fuel sender, there may be a problem with the float. If it fell off then it could read about anywhere on the gauge. When they get a pin hole, they sink to the bottom.
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Old 05-26-2019, 10:43 PM   #17
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Default Re: Runtz Failures

  • Your originally 6v (nominal) battery had dang close to 8v with the engine at highway speed.
  • Your originally 6v (nominal) battery had almost 6.5v at full charge sitting idle.
  • KS gauge reading difference are insignificant from 5v to 8v
So, install one ($15 new) Ford Mustang or Galaxy module (photos above) which the factory used on early 12v (nominal) cars equipped with older 6v gauges and tozz the runzz. 1960 (nominal)


  • If you feel the readings are incorrect at 8v you have a sensor or gauge problem.
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Old 05-27-2019, 12:09 PM   #18
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Default Re: Runtz Failures

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Originally Posted by Red98 View Post
  • Your originally 6v (nominal) battery had dang close to 8v with the engine at highway speed.
  • Your originally 6v (nominal) battery had almost 6.5v at full charge sitting idle.
  • KS gauge reading difference are insignificant from 5v to 8v
So, install one ($15 new) Ford Mustang or Galaxy module (photos above) which the factory used on early 12v (nominal) cars equipped with older 6v gauges and tozz the runzz. 1960 (nominal)


  • If you feel the readings are incorrect at 8v you have a sensor or gauge problem.
You and Flatheadmurre are correct. The gauge deflection is not affected by the source voltage, at least within the 6 to 8 volt range. I get the same incorrect reading on both 6 and 8 volts.

I checked the ground at the gauges and no problem there. I will try different oil pressure and temperature senders to see if that helps.

If it turns out to be the gauges, I will just learn to live with gauges that are not correctly calibrated.
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Old 05-27-2019, 02:52 PM   #19
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Default Re: Runtz Failures

The GROUND in question is NOT at the gauge but at the SENSOR i.e. ENGINE.
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Old 05-27-2019, 03:16 PM   #20
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Default Re: Runtz Failures

Yes, the sender/sensor IS the ground path for the gauge. The sender/sensor regulates the current flow to ground. That current flow through the gauge heats a coil which bends a bi-metal connection to the indicator. In the original senders a set of points open and close at a various rates to control the current through the heater coils. Reproduction senders use variable resistance to control the current flow.
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