Fuel gauge mystery

[GB SISSON]

Background: '47 half ton, 12 volt neg ground, runtz units on each gauge from 5th ave garage. Tanks inc poly tank with their supplied 'ford sender'. Sender is grounded to frame with clean grounds, new wire. When first set up last summer all gauges worked correctly. Recently the fuel gauge stopped working. I took the instrument panel out and it passed the D-cell test perfectly. While the panel was still out I reconnected all wires and the fuel gauge worked properly as before. I don't really like it when stuff fixes itself and I can't see why. OK, so now it works once more and so I reinstall the gauge cluster and now the fuel gauge doesn't work again. No wires amiss, everything installed well. So Out it comes again. With it out of the dash the fuel gauge and all the other gauges work well. Only thing I can think of is it grounding to the dash changes something. I then hook up a jumper to ground and the frame of the instrument panel and the fuel gauge drops to empty (tank is full). So, in review... With the instrument panel out of the dash and dangling from it's wires, all is well, re-install it and the fuel gauge doesn't work. Wasted all morning taking it in and out. I need some advice. Thanks.

[40cpe]

Just a wild guess, but you have reversed the polarity. I don't know if that makes a difference on King-Seely guages or not.

[GB SISSON]

The suspense was killing me so I tested and tried a fuel gauge from a parts truck. Same exact thing. Thanks 40cpe, but in all the many articles and posts about 12v neg conversions that I've read, it's always, reverse the wire through ammeter, change bulbs etc, nothing about re-wiring the gauges backwards. Are the gauges sensitive to which side gets power and which side goes to sender? I was very careful when I added the runtz units, but I could have gotten one wrong.

[BillM]

My experiments with King Seely gauges show that polarity doesn't matter. The deflection of the needle in the gauge is due to the heat generated by the coil in the gauge, there is no magnetism involved and the gauges worked with either polarity on the bench. I think your problem is wiring or somehow the studs on the backs of the gauge are not isolated from the panel.

[cmbrucew]

Ground your instrument cluster. Drill a hole in the body somewhere under/ behind the dash, and use a star washer with bolt/screw to create a good ground for it
Bruce

[GB SISSON]

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But when the panel is grounded the fuel gauge doesn't work. It's more like I want to insulate the panel from the dash, because that's when everything works. ??? I have to do a lumber run to the mainland tomorrow so I will continue my quest for a working fuel gauge over the weekend. Thanks all, and keep scratching your heads.

[Milt K from Pa]

GB
Could one of the meter screws insulating washers for voltage and the signal studs have split allowing one of them to short to the meter case and thereby, grounding the signal??? Check for resistance to the meter housing from each meter stud (wires disconnected), I would think there should be infinity to case. This all assumes a metal meter housing.
I've never used a Runtz unit, maybe some electrical miss-connection concerning it's grounding??

Milt K from Pa

[GB SISSON]

Originally Posted by Milt K from Pa

GB
Could one of the meter screws insulating washers for voltage and the signal studs have split allowing one of them to short to the meter case and thereby, grounding the signal??? Check for resistance to the meter housing from each meter stud (wires disconnected), I would think there should be infinity to case. This all assumes a metal meter housing.
I've never used a Runtz unit, maybe some electrical miss-connection concerning it's grounding??

Milt K from Pa

With both gauges acting the same, maybe you are onto something with the runtz on the fritz theory.....The runtz attaches to the stud and has a forked grounding tail that goes under a mounting screw head.

[Brian]

I seem to recall that when I fitted Runtz's into my 12 volt converted 35, I had to reverse the wiring to the fuel gauge in order for it to work.

[flatheadmurre]

Gauges don´t care about polarity.
What happens when you install the panel, if the gauge goes the same way as if you ground the lead at the sender you probably have a short between the sender post on the back of gauge and the panel.
But for the voltage reducers to work don´t they need ground...are they working as they should with the panel in the air ??

[Paul Bennett]

Some voltage reducers such as the Runtz which use semiconductor voltage regulators DO require a negative ground to work.

RUNTZ

+More ammo for me not converting to 12v.+

[51 MERC-CT]

Don't know why anyone needs to use a "Runtz" reducer on each gauge when a single reducer for all the gauges that Ford uses from '56 to well into the '60's to reduce voltage to the gauges is available and it works.
Mine has worked for over 20 years.

[19Fordy]

Wonder what would happen if you used a Constant Voltage Reducer (VCR) and the OEM KS gauge instead of the Runtz set up? I have been using the Ron Francis VCR and the OEM fuel gauge since 1999. Works great. I am very surprised that your "Tanks Ford sender" works accurately with the OEM fuel gauge since the KS gauge and sender work on a "bi-metallic" heat principle - not ohms resistance. Hope you are able to solve the mystery. If you use a 6V dry cell instead of the D-Cell, will the gauge function properly? You can buy one at Lowe's. Here's info on the Tanks sending unit.
http://www.tanksinc.com/index.cfm/pa...cat/cat159.htm

[Drbrown]

I'm with the idea of a gauge post getting grounding when you install the panel in the dash, otherwise I would try switching your three Runtz units around to see if you get different results. My Runtz units have been in my car for decades and provided they are grounded, they are pretty faultless. They are not polarity conscience. It's pretty hard to damage or burn one out.

[GB SISSON]

When I get out to the shop I will try swapping the runtz units around and see if I can isolate what's going on. Thanks for all the replies. The generic 'ford type' sender from tanks inc worked about like many of here said. It gives an indication of what's going on, which is better than nothing. I did try a good old KS sender that I found and it runs through perfectly, but won't mount in the tanks inc tank without major surgery. BTW, it acts the same as the other one as far as quitting when grounded, so it's gauge related. The wire between gauge and sender is new and nicely routed, no shorts.

[JSeery]

Have you checked the sender post on the gauge to the gauge case to see if the post is shorted to the case? Need to check it with the sender wire disconnected.

[GB SISSON]

Originally Posted by JSeery

Have you checked the sender post on the gauge to the gauge case to see if the post is shorted to the case? Need to check it with the sender wire disconnected.

I am quite challenged with electricity. I have taught myself a lot over the years, but don't know how to do this check. I have the first KS fuel gauge that started this mystery out and sitting on the bench. I can test the other one too. I do have a tester with res and black leads, and a rotating dial for volts etc. It is digital. The gauge acted the same with either gauge. Haven't had a chance yet to switch runtz units around. Been unloading and sorting lumber I picked up yesterday. No real Saturdays for the self employed, never mind 'retiring' someday.

[cmbrucew]

Gary
For this kind of work, I think the analog tester is more reliable than your digital.
Bruce

[rotorwrench]

The ground polarity is important to a switching voltage regulator and that's why they have a ground wire on the Runtz. Make sure that the screw stud terminal on the runtz does not make contact with any of the surfaces of the gauge that can ground the 12-volt input. Make sure that each runtz unit has its own power wire coming from the power source wire. They can not be connected in series with other units, only in parallel with the original power wire unless they already were connected each to their own power wire.

If all the wiring is correct then there is likely a problem with the way the runtz was made, ie one of the connectors to the little voltage reducer was miss-connected for proper operation. These things only work with negative ground 12-volt systems but it sounds like that's the way the vehicle already is set up.

[47Merc]

I changed my single gauge 12 volt reducers to one of these for all the gauges and it works great.

https://www.macsautoparts.com/ford_m...es-439368.html