For thousands of automotive professionals, the Sun machine was more than a piece of equipment—it was a symbol of professionalism, technical expertise, and a better way to diagnose vehicle problems.

Long before computerized diagnostics became standard, Sun Electric Corporation was teaching technicians across America and the world about a simple but revolutionary concept:

"Test, Don't Guess."

Many of us who worked for Sun, sold Sun equipment, or relied on Sun products in our shops remember a time when a Sun Motor Tester was the centerpiece of every professional service department. From dealerships and independent repair facilities to fleet maintenance operations and military installations, Sun equipment helped define modern automotive diagnostics.

But how did it all begin?

The story begins in Chicago with a man named Otto L. Rhoades, founder of what would eventually become one of the most respected names in automotive testing equipment.

Historical records confirm that by 1936, Rhoades was already manufacturing and distributing engine diagnostic equipment through a company known as Sun Manufacturing Company. One of the earliest documented references appears when the University of Notre Dame acknowledged receiving a Sun Combustion Tester from Rhoades for its Aeronautical Engineering Department.

At a time when many mechanics relied on experience, instinct, and trial-and-error repairs, Rhoades envisioned something different: scientific diagnosis.

That philosophy would become the foundation of Sun Electric.

Throughout the late 1930s and 1940s, Sun expanded its product line beyond combustion testers into a complete range of diagnostic equipment.

As engines became more sophisticated, technicians needed tools that could accurately evaluate ignition systems, charging systems, vacuum performance, compression, dwell, timing, and distributor operation.

Sun delivered.

The company's products allowed mechanics to identify problems before disassembling an engine, saving customers money while increasing shop productivity. The result was a dramatic shift in the automotive service industry. Instead of replacing parts until a problem disappeared, technicians could diagnose issues scientifically and repair them correctly the first time.

For many shops, Sun equipment became a competitive advantage.

By the 1950s and 1960s, Sun Electric had become a dominant force in the automotive service industry. The company's headquarters at Harlem and Avondale in Chicago became the center of an expanding operation that included manufacturing facilities, engineering departments, sales offices, and service centers throughout North America and around the world.

Former Sun employees remember a company culture built around innovation, training, and technical excellence. 

Whether you were a factory employee, field representative, service technician, trainer, distributor, or customer, Sun represented quality.

The famous Sun Motor Tester became an icon of professional automotive service.

Walk into almost any dealership service department during that era and you would likely see a Sun machine standing proudly in the service bay.

Many people remember Sun strictly as an automotive company, but Sun Electric's capabilities extended far beyond automobile repair.

The company manufactured equipment for:

• Automotive diagnostics
• Fleet maintenance operations
• Aviation testing
• Industrial testing systems
• Military applications
• Government contracts

By the 1960s, Sun was producing sophisticated electronic, electrical, hydraulic, and electromechanical testing systems that served customers well beyond the automotive aftermarket.

This diversification helped establish Sun as one of the most technically advanced diagnostic equipment manufacturers in the world.

Anyone who worked for Sun during its peak years knows that the company's success was built on more than great products.

It was also built on people.

Sun's 600+ American sales representatives (Zone Managers) became trusted advisors to dealership owners, service managers, vocational schools, fleet operators, and technicians.

Many former Zone Managers still recall traveling across their territories demonstrating equipment, conducting training programs, and helping customers improve shop productivity.

Relationships mattered.

Technical expertise mattered.

Integrity mattered.

Those values helped build one of the strongest brands in the automotive service industry.

In October 1992, a major chapter in Sun's history came to a close when Snap-on acquired Sun Electric for approximately $115 million.

For many longtime employees and customers, the acquisition marked the end of an era.

Yet it also ensured that Sun's technology, engineering expertise, and diagnostic innovations would continue under a larger global organization.

Many of Sun's diagnostic systems, emissions-testing technologies, and information systems became important components of Snap-on's growing diagnostics business.

While the corporate structure changed, the Sun legacy continued.

Today, younger technicians may never have experienced the excitement of seeing a Sun Motor Tester diagnose an engine problem in real time.

They may never know what it was like to attend a Sun training seminar, watch a live product demonstration, or see a dealership service department centered around a row of bright red Sun machines.

But those who lived through that era understand something important:

Sun Electric helped transform automotive repair from an art into a science.

The company's influence can still be seen in every scan tool, every computerized diagnostic system, and every technician who believes in testing before replacing parts.

The technology has changed.

The philosophy has not.

More than ninety years after Otto L. Rhoades began building diagnostic equipment in Chicago, the lesson remains as relevant as ever:

Test. Don't Guess.

For former Sun employees, customers, distributors, and friends, that simple principle remains one of the most enduring legacies in automotive service history.