another electrical question - fuel gauge voltage

Hi guys,
Just want to determine the correct voltage for the fuel gauge unit. Most cars are 5 volts, but looking at my official diagram, it appears to be 12 volts. I am running a repro fuel sender from that guy on ebay.
Also, there is a resistance wire at the temperature sending unit - is this a substitute for a 5 volt supply - as in the voltage is dropped at the sender to avoid damaging the temp gauge?

My plan is to build an electronic voltage regulator for the dash 12/5 volts like on cars, and use this to power my gauges.
Looking forward to some replies

fuel and temp gauges run a small voltage limiter on the back of the cluster @ 5v but the resistance wire is to steady the temp gauge from wild swings, at least thats how mine runs.

Dont know about voltages?? Yet do know every fuel gague ive tested was an electrical Pulse type from gague to sender=meaning when testing to see if voltage was present from gague to sender-(wire to sender unhooked) the test showed only a pulse -on/off/on --- not contunious voltage as I was expecting.

Mopars run a voltage limiter on the back of the cluster that feeds the fuel and temp gauges. Nominal voltage is 5 volts, and it's NOT solid state, so you can see the voltage pulse.
I found this online

GM fuel tank senders used 10 to 30 ohms until 1964 and then went to 0 (zero) ohms and to 90 ohms when full.
Ford fuel tank senders will read zero ohms at empty and 73 ohms at full.
Most muscle era Mopars fuel tank sending unit has a resistance range of 10-73 ohms. OR Tank empty 55 ohms, full 8 ohms.
Stewart Warner fuel senders are 240 ohms at empty and 33 ohms at full, although there is an “acceptable” variation of 10 ohms either direction.

Other things I have read indicate that Mopars are 'backwards' from the others, making it smart to check YOUR sending unit to make sure. It's also often on the wiring diagram so check that too.
If both gauges do not work, check the voltage limiter. If only the gas gauge doesn't work, it's most often the sender, the float or a poor ground.

read here - https://vintage-vans.forumotion.com/t1077-gauge-problems - oo3

oo3 wrote:read here - https://vintage-vans.forumotion.com/t1077-gauge-problems - oo3

Thanks, I had already downloaded instructions to build a 7805 regulator, and it was a guy who has a Dodge who posted the info

I didn't know about the internal regulator within the fuel guage - that answers my question entirely, as I was aware that most fuel & water temp gauges run on 5V. Thanks also for above the reasoning behind the temp gauge resistance wire - another helpful tip learned.

I had been running a MoPar 5V regulator, and I thought it had blown, so I opened it carefully this morning, and I can see how they work - bi-metal strip with a resistor coil heats up and breaks contact, giving the effect of a chopping 5V to 0V constantly, as opposed to a steady regulated solid state output 5V.

Thanks guys, this really is a huge resource of info

RodStRace wrote:............... If only the gas gauge doesn't work, it's most often the sender, the float or a poor ground.

Thanks again....I just discovered I don't have a ground wire. However, the gauge has been working up until last week. I figured there is grounding between the tank and the straps as it is all freshly cleaned etc - but I will install a wire as well.

It's a little metal strap that goes between the sending unit fuel line, over the rubber hose to the body fuel line.

Here is some details on the problem: link

Depending on the year you may have an external "gauge voltage limiter" screwed to the back of your instrument cluster or it may be an internal unit that is inside the fuel gauge. My '65 has the unit inside the fuel gauge, 12v goes into the fuel gauge and then a 5v jumper wire goes over to feed the temp gauge.

Taking a reading off of your sending unit wire, a full tank will read 9 to 10 ohms, an empty tank will read 96 to 98 ohms, 1/2 tank will be 60'ish ohms. You should have a fluctuating 2-5v coming out of your gauge voltage limiter, if you put a solid 12v on those gauges you'll let the magic smoke out.

If the internal limiter is bad you can send the gauge off and have it bypassed and use an external limiter. If you have an external and its bad just replace it:
NAPA has the Echlin brand, part number "IR9" for $43.00
Pep Boys has the Borg Warner R-307 unit for $35.00
Duralast Wells at auto zone: $38.00 Pn: IRV307

D&M Restoration can test/repair your gauges if needed, I sent them one of mine and had the internal limiter bypassed and the ohm readings verified.

D&M

If you don't have the metal ground strap for your tank you can use a hose clamp on the sending unit neck to clamp a wire on and then use a ring terminal and self tapping screw to ground it to the frame.

Here's some more how to fix it stuff from Allpar:
link

Also, if you replace your mechanic voltage regulator on the firewall with a solid state one it will pretty much stop your gauge/light flutter (due to pulsing output from the alternator).

OK, well I built my solid state 5V regulator, and now it feeds my gauges. And whatdayaknow...the fuel gauge works

I will post pics shortly, as I have by-passed the 12V side of the fuel gauge, and looped off to feed the oil & temp gauges. Followed the link and instructions from AllPar site, and it works great. My only concern now is that I may have to calibrate my sender unit, by adjusting the arm on the float. Better get some miles on the road first, and chew some gas....it's a real bi7ch to syphon

Thanks for all the input above, plenty to think about for all situations.

BTW, I am running a 100Amp one-wire alternator with a built in regulator - Powermaster brand from Summit Part No.TFF-7509REDP, $125 roughly plus shipping.

bought repro sender also - https://vintage-vans.forumotion.com/t5952-fuel-tank-sending-unit-leak?highlight=sending+unit - tried to adjust - but still must have at least 5 gallons just to get up to e - depending on tank you may or may not have to drop it- i did not - did you have to mod anything to fit that alt ( besides wiring) - oo3

That's not a bad thing, considering the pickup/outlet is not at the bottom and it gives you a bit of emergency reserve. Jeeps are famous for running out at an 1/8th of a tank!

oo3 wrote:bought repro sender also - https://vintage-vans.forumotion.com/t5952-fuel-tank-sending-unit-leak?highlight=sending+unit - tried to adjust - but still must have at least 5 gallons just to get up to e - depending on tank you may or may not have to drop it- i did not - did you have to mod anything to fit that alt ( besides wiring) - oo3

Just read that thread, and I too had problems with my new repro sender unit. The lock rings really are a bunch of carp, and I ended up using the new rubber gasket with the old lock ring - not ideal, but I didn't want leaks. I did actually test the sender at the time, and played with the arm a little bit, as I had done similar adjustments on my GTX, and a friend's Challenger.

As far as the alternator goes, I ditched the existing regulator on the firewall - easier since I made my own new loom for the entire truck. Those cables get awfully crusty after 40+ years, and I measured out my temp gauge resistor wire - 5 ohms, so I replaced it with a 5Watt block resistor. I had been running with that resistance wire carefully wrapped around a small piece of conduit pipe, but it looked ugly.

So I ran up the engine last night for the first time in a month, and it ran sweet. The temp gauge came up to half after about 5 minutes, and the oil gauge reads about the same, but responds very quickly. My oil gauge replaced the old warning light - never trusted a light, I like to see some action But the oil gauge I bought off fleabay was toast (advert said good driver condition, untested ) - so I took a chance. Well it didn't work, and appears to not have worked for some time - burnt out coil inside. So here's where I got cunning like Wile Coyote......I scavenged a temp gauge out of an old Australian Valiant ( like a Dodge Dart) and grafted the fleabay Oil gauge face onto the 'new' temp gauge. These gauges are near enough identical, so don't get fooled into paying huge money for a very rare oil gauge. The temp gauges are the same, and of course it runs off my newly built 5V regulator. The only thing wrong with my Oil gauge now, is there is no legend on the face, only the marker lines.

My truck in Oklahoma the day the deal was done...


one month after it landed here...


Dash layout as when I bought the truck - pre-restoration...




dash panel removed for mods...


Fuel gauge showing the by-pass of 12Volts... Connect the original 12V feed to fuel gauge to the multi-port terminal at the back of the Amp gauge - make sure the connection to the fuel gauge is broken...


my dream oil gauge....


cluster in bits a while ago....


Alternator complete with brackets by BPE as part of Air-con installation...




I will repeat this tip in the section as a header so anyone else watching can think about it

nearly forgot the latest pics of my dash....

thought I saw that truck on ebay a while back?

Not this one....bought this truck off one of those online trader type sites in Arkansas in July 2009....wow that's 2 years now