The Stovebolt Site Forums The Shop Area The Electrical Bay 6 Volt Positive Ground Fuel Gauge

Does anyone know if it’s possible to convert a 6 volt negative ground fuel gauge to a 6 volt positive ground fuel gauge? Or is there some kind of converter that could be used inline to make this work?

This is for a 1950 GMC 1/2 ton.

Thanks in advance.

If you are converting the truck to negative ground, there is nothing you need to do to the fuel gauge wiring. Be sure you know what you are doing when converting. This Tech Tip will tell you what to do. It's short and simple. It's at the begining of the 12V conversion tip.



https://www.stovebolt.com/techtips/12_volt_conversion.html

I’m wanting to keep it positive ground. I posted earlier a description of what was going on exactly, but the admins moved it to the swap meet forums. Here’s what I originally posted that’ll provide some context.

“I’ve got a 1950 GMC 1/2 ton that I’ve completed a frame off restoration on, that is still 6 volt. However, I’ve had to switch it to negative ground, solely because of the fuel gauge. I’d like to switch it back to positive ground. So I’m looking for a 6 volt fuel gauge, that is positive ground, as original. I’ve purchased 2 new 6 volt gauges, from two popular vendors, but the gauges do not function with positive ground. I called and had a lengthy discussion with the owner of the Filling Station about this, and through his research he got back to me confirming that the manufacturer of the “new 6 volt gauges” is for negative ground only.”

It looks like I might be able to use a “buck boost converter” to accomplish this. I’ll do a little more research into that.

Don't think that sounds correct.. Jim Carter sells the same 6V gauge for both Chevy and GMC, 1950

Also this

If a person is converting to neg ground, the sender wire still goes to the gauge sender terminal, the power (ignition switch "ON") still goes to the gauge power terminal and gauge frame needs ground. You don't change gauge polarity, you change battery polarity. Like light bulbs don't need polarity change. Just battery, coil and probably ammeter need polarity change. You don't change any other polarity.


In your case, you are putting everything back the way it was, (positive ground) so actually no change from original. Sounds like you got messed up when you thought you had to convert to negative ground for the gauge. That was wrong info unless there is something/some action you don't include here. Put the battery back to pos gnd, coil back to pos gnd, and report results before moving forward. What exacly did the gas gauges do, that you say "do not function"?

In addition to the items bartamos listed above, don't forget to change the polarity of the generator after installation and battery hookup. Jump the ARM terminal to the BAT terminal for a half second.

Bartamos, I just looked at the gauge you linked, that Classic Parts sells and it states that it “Does not work with original positive ground trucks”, shown circled in red on the photo.

Phak1 you are correct. I am 100% positive that the new gauges will not work with positive ground. As I mentioned I had the owner of the Filling Station confirm this with who ever he purchases the gauges from.

Classic parts was the other vendor I tried. I think they added that it will not work with positive ground in their description after the discussions I’ve had with them.

Bartamos, when hooked up with positive ground, the gauge does nothing. It just stays in empty and does not move.

I’m exploring the idea of a buck boost converter. It sound like that may be the answer.

Thanks Phil.

Jake, What is wrong with converting to neg ground?

Bartamos nothing wrong negative ground. I’ve had it negative ground for about 2 years now. However, when I finished the restoration 2 years ago, I purchased a Pertronix unit for it, now it just sits on my shelf solely because of the fuel gauge. My goal with the restoration was to get as close to original as possible, with a few safety upgrades, and the pertronix ignition was one of those.

I wouldn't consider Pertronix to be an upgrade. Changing to negative ground makes more sense than adding a Pertronix system.

To each his own. I have another vehicle with Pertronix. Never had an issue. Two others with points. Never had an issue with those either.

Yes you can convert those from negative to positive ground. you need flip the coil wiring.
The applies for a gauge going from negative to positive or positive to negative.

check your gauge as coils in the below are top and bottom but you can just look at wiring and determine which one is which based on which one is wired to case vs pins.
This was written up for a guy converting a British car but still applies.
i know several guys that used this to go from positive to negative. you would just his instructions backwards on negative to positive.

Please post a picture of your gauge from the back that you want to convert.

Get the instructions with pictures below link as it applies to any coil type fuel gauge. Yes its a boat car but his writeup is excellent and like i said a few car buddies of mine who love restoring British cars use it to convert to negative ground because of the electronics and his other explanations like not blowing up phone chargers. Your just doing the same thing on a negative ground gauge.

https://www.amphicars.com/tech/default.html

Fuel gauge section is about halfway down the page. under his tech section.

if you find a NOS that would work to like posted above and play with one of the gauges you bought

So now you are saying that the Pertronix is for a positive ground and if you go to neg ground you can't use it?

If there are parts available that will work for neg ground but if you go pos ground you can't find parts now or in the future (if they go bad).....go neg ground now. Buy whatever you need off the shelf. That will be plenty original and a much better solution than screwing around/running around/modifying with unknown results. The whole USA went neg ground soon after your truck was built.

Nothing wrong with Pertronix now a days. Many bad reviews are user errors or miswire or ballast resistor misunderstanding or older versions of Pertronix.

You are in a twisted trap. Go neg ground and get out of it. Buy what you need, sell the rest.

But it's your truck, your money and your decision. I support you, as you protect our community each day. I'm in AZ
WOW I see I "helped" you way back in 2019. Confusing, back then you said ... "I’ve got a question about wiring my stock ammeter (1950 GMC Truck) to my 12v , 3 wire GM alternator (sbc 350)" ?????????????? Now that truck is a 6V positive ground 6 cyl? "Pat, I'd like to solve the puzzle"

Bartamos, I do remember posting something about this issue back then, but I’d have to go back and see exactly what it was. The truck with the 350 you’re referring to is also a 1950, but it’s panel truck that’s kind of a resto mod. I do remember asking questions about that one as well, but again the details escape me. Like you said I think it was about using the stock ammeter with a GM alternator, which has worked great since 2019 or whenever it was I finished that project. I still drive that quite a bit to this day.

This issue with the fuel gauge is a few years old, and I only asked about it because I saw the pertronix unit collecting dus on my shelf, and thought I’d resurrect it and see what I could figure out this time around. Like I mentioned, I’ve been driving this truck (restored one) for a few years now with points, and negative ground. I have no issues doing that. I just figured since I have the pertronix, why not try to utilize it? The fuel gauge was the only thing preventing me from doing that. I did try to sell the pertronix for a bit, I think I had it listed on this site and oldgmctrucks, but it never sold. So it sat on my shelf. That brings us to today.

The fuel gauge will only work with negative ground, and the pertronix will only work with positive ground, so it’s one or the other. I just thought I’d throw up a post and ask for some advice again, and see if I could get any new information. It really doesn’t bother me to run the truck with either ground set up. If I can make everything work together, great. If not, the pertronix will continue to sit on my shelf, and I’m out the $150 or whatever it cost me years ago.

When I first explored this years ago, I thought exactly like you did, that the polarity would not affect the fuel gauge. And I kept being told that on the forums. However, the practical side of this was not working on my work bench, as I purchased two fuel gauges from two different vendors, who both told me they should work. But they didn’t. That’s when called Steve at the Filling Station, and was great as far as wanting to get to the bottom of this for me, so he called his supplier/vendor for the new gauges he sold, and was told that in fact these new gauges do need the correct polarity in order to work, which is of course negative ground.

I figured maybe I’ll get to the bottom of it this time around. And maybe help someone out in the process who might be having the same issues I’m having.

Here’s the restored truck in question.

Also attached are a few photos of the panel truck with the vortec 350 in it.

Nice work on both trucks. I would not use the old Pertronix anyway. It may be back in their early non reliablity days. Let me know what you decide to sell and I will help sell. If that is 4peaks I see, I'm guessing Rio Verde. A neg ground 6 cyl Pertronix mechanical advance is $85 on Amazon. They are all 12V and they say contact them for 6V.

If it ain't broke, don't fix it.

That pickup is beautiful.

Thanks gents, I appreciate it. And thanks to all who reached out offering suggestions. Still not sure what I’m going to try next, but I’ll keep you posted.

Bartamos, I’m a little further south than that. I live in Green Valley, just south of Tucson. It’s a beautiful area close to the San Rafael Valley.

Otto, He says just revisiting the situation to see any new ideas. So, no new ideas. Unfortunately.

Pertronix says only 90 day return, in good useable condition and may charge restock. I don't deal with companies like that, especially when they warranty short periods.

Points are good, neg GND is good. Pretty "GM" stock that way. Carry a condensor with you. Just consider GMC's idea a mistake that you don't want to repeat.