When a 1957 Positive-Ground Car Meets a Modern Negative-Ground Radio
Updated: Sep 11
One Simple Mistake Became One of My Best Restoration Lessons
Sometimes the Best Restoration Stories Begin With a Mistake
One of the reasons I wanted to create Fitzgerald Classics wasn’t simply to showcase beautifully restored automobiles.
There are already thousands of websites that do that.
I wanted to build a place where enthusiasts could learn from real restoration experiences—the victories, the setbacks, and the unexpected lessons that happen in every garage.
This week’s story is one of those lessons.
It started with something as simple as installing a radio.
Keeping Yesterday’s Appearance With Today’s Technology
One of the current Fitzgerald Classics projects is my 1957 Nash Metropolitan.
The goal has never been to build a modified hot rod.
Instead, I’ve tried to preserve the character of the Metropolitan while making a few carefully chosen upgrades that improve drivability without changing its personality.
One of those upgrades was the radio.
Rather than installing an obvious aftermarket stereo, I purchased an original Metropolitan radio that had been professionally converted internally with modern AM/FM electronics.
From the dashboard, it still looks exactly like Nash intended in 1957.
Hidden inside is modern technology.
To me, that’s the best of both worlds.
Before It Goes In The Car…
Whenever I install an electrical component, I always bench test it first.
It’s a simple habit that has saved me countless hours over the years.
A bench test lets you verify everything works before crawling under the dashboard, fighting wiring, and wondering later whether the problem is the component—or your installation.
So that’s exactly what my son and I did.
We connected the radio to a regulated bench power supply.
Then we made one very reasonable assumption.
It turned out to be wrong.
The Metropolitan’s Positive-Ground System
Like many British and British-derived automobiles of the 1950s, the Nash Metropolitan uses a 12-volt positive-ground electrical system.
That means the chassis is connected to the positive battery terminal.
Since we knew the Metropolitan was positive ground, we wired the radio that way.
Everything looked correct.
We flipped the switch.
Nothing.
Well…
Almost nothing.
The dial light illuminated.
The radio itself remained completely silent.
No static.
No music.
Nothing.
The Label That Changed Everything
Rather than assuming the radio had arrived defective, we took a closer look.
Stamped clearly on the radio was one simple instruction:
NEGATIVE GROUND ONLY
We looked at each other.
Swapped the power leads.
Turned the radio back on.
Instantly…
Music.
Crystal-clear FM reception.
Excellent AM reception.
Perfect sound.
The radio worked flawlessly.
Did We Damage It?
That question bothered me for quite a while.
After all, we had accidentally connected the radio backwards for approximately fifteen minutes.
Had we shortened its life?
Was hidden damage waiting to appear later?
Fortunately, every indication says no.
The fuse never blew.
The radio never overheated.
Every function worked perfectly.
AM reception was excellent.
FM reception was excellent.
The audio quality was exactly what it should have been.
Why?
Most professionally converted radios include reverse-polarity protection to prevent accidental damage.
Had that protection not existed, we likely would have known immediately.
Instead, once the polarity was corrected, the radio behaved exactly as it should.
Sometimes you get lucky.
Sometimes good engineering saves the day.
Why Doesn’t Simply Reversing The Wires Work?
This is one of the most common questions asked by owners of positive-ground vehicles.
At first glance, it seems logical.
“If my car is wired backwards, can’t I simply wire the radio backwards too?”
Unfortunately, modern electronics don’t work that way.
Today’s radios are designed around a negative-ground reference.
Their internal circuit boards, voltage regulators, audio amplifiers, and electronic components all assume that the radio’s chassis is connected to battery negative.
Simply reversing the power leads doesn’t change the internal design.
It simply applies reverse polarity.
In many cases, that permanently damages the electronics.
Fortunately, ours survived.
The Right Way To Solve The Problem
Owners generally have two options.
Option One
Convert the entire vehicle to negative ground.
Many Metropolitan owners choose this route.
It allows virtually any modern accessory to operate normally.
However, it also requires modifications to the electrical system and moves the car away from factory originality.
Option Two
Leave the car completely original and install an isolated positive-ground to negative-ground power converter for the radio.
This is the approach I plan to take.
The converter creates a separate negative-ground power supply for the radio while leaving the rest of the Metropolitan exactly as Nash engineered it.
Original appearance.
Modern functionality.
No compromises.
What I Learned
This experience reinforced something I’ve learned repeatedly during restoration work.
Never assume.
Always verify.
Had we read the label before applying power, we would have avoided fifteen minutes of confusion.
Fortunately, the radio’s built-in protection did its job.
But not every electrical component is that forgiving.
One extra minute of checking can save hundreds of dollars.
Fitzgerald Insight
Classic car restoration isn’t about never making mistakes.
It’s about learning from them.
Every project teaches us something.
Sometimes it’s how Chevrolet stamped casting dates.
Sometimes it’s the proper routing of a PCV hose.
Sometimes it’s discovering that a radio which looks exactly like it belongs in 1957 actually thinks it’s living in 2026.
Those lessons become part of the restoration.
More importantly, they become knowledge we can pass along to the next enthusiast.
If my mistake prevents someone else from damaging an expensive radio, then sharing the story was worth it.
Final Thoughts
One of the goals of Fitzgerald Classics is simple.
I don’t want this website to become another collection of specifications and torque charts.
I want it to become a place where enthusiasts can learn from real experiences.
Sometimes those experiences involve beautiful concours-winning restorations.
Sometimes they involve chasing an electrical problem around the garage for an afternoon.
Both have value.
Because every classic car has a story.
And every restoration teaches us something.
This week’s lesson reminded me that preserving these automobiles isn’t just about maintaining old machinery.
It’s about preserving the knowledge that keeps them alive for the next generation.
About the Author
Dan Fitzgerald is the founder of Fitzgerald Classics, a Veteran-Owned publication dedicated to preserving America’s automotive heritage through honest restoration stories, practical technical guidance, and real-world experiences. Whether documenting a numbers-matching 1966 Corvette or bringing a 1957 Nash Metropolitan back to life, Dan believes every project offers an opportunity to learn, share, and inspire others to preserve the cars—and the stories—that shaped America.
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