Jim Smart
October 5, 2016

One of the least understood components in a classic Mustang is the electric clock. During all the years Ford produced classic 1965-1973 Mustangs with electric clocks, these Borg Instruments clocks didn’t change much mechanically. In fact, in many applications Mustangs share clock movements with GM, Chrysler, and AMC.

Although called “electric” clocks, these classic automotive timepieces were actually wind-up clocks like the Big Ben you’d have sitting on the nightstand back in the day before digital time telling. What makes these clocks “electric” is that brief nanosecond moment when a solenoid (electromagnet) rewinds the clock’s main movement to keep the balance wheel dancing and movement rolling.

If you were around a half-century ago, you probably remember the steady tick-tick-tick sound of a car clock, especially if you were sitting in a luxury car. Every minute or so, you heard an audible click of the electric rewind solenoid. That’s what made these clocks electric and what also made them easy on your car battery. The rest was a mechanical wind-up clock movement subject to all of the failings of a wind-up clock. To add insult to injury, these sensitive movements were exposed to extremes of heat, cold, dust, and crud. Few of them lasted any time at all before they stopped and motorists began looking at their watches during the drive.

Car clocks fail for a variety of reasons: main and return spring failure, burned contact points, solenoid burnout, an open circuit, mechanical seizure, and more. The most common failures we see are contact point burning and pitting along with some kind of mechanical failure. Because the solenoid’s positive lead from the power post is hair thin, it can break, rendering the clock inoperative.

Classic Mustang clocks appear complex, but they’re actually quite simple. And although we could show you how to take one apart and rebuild the movement, you’re better off shipping your Mustang’s clock to a professional shop like Instrument Services (which is very familiar with these timepieces) or convert to a quartz movement yourself. Instrument Services will tell you that car-clock rebuilding and adjustment is not for the novice. However, we can show you how these dusty old movements work, where to get parts, and how to wake up a sleeping electromechanical period clock.

01. This is a 1967-1968 Mustang clock. All 1965-1973 classic Mustang clocks have this same Borg Instruments electromechanical clock movement regardless of the clock size. You will know it’s a Borg clock by the letter “B” on the back cover next to the Ford part number. The cover is removed by bending two tabs at the perimeter, which frees the cover.

02. These are closed contact points, which complete the rewind solenoid circuit firing the solenoid and rewinding the clock movement. When these contact points become pitted and burned, they stop making contact and the rewind solenoid stops working. In due course, the clock winds down and stops.

03. Here are the contact points in the open position after a solenoid rewind. As the clock movement progresses, the contact points head back to close and automatic solenoid rewind. As the clock ticks, the balance wheel brings the points back to close.

04. Here, the contact points are closed again. The key to clock function is clean contact points. Although some suggest working the contact points with an emery board, it’s best to use a small fine file, which is less likely to leave contaminating residue in the contacts. When contact points are badly damaged, send your clock off to a professional repair shop, such as Instrument Services.

05. From this angle, you can see the clock’s traditional balance wheel and spring. The balance wheel is something of a flywheel that rocks back and forth with help from a tiny hair-like spring to keep the movement going. As the balance wheel rocks back and forth, the return spring brings points back to contact and electric rewind.

06. This is the electric rewind mechanism and return spring.

07. Here’s one example why a clock stops—a broken return spring. When this spring breaks, the points will not return to close (rewind).

08. This is the rewind solenoid (electromagnet). Contact points close to send 12 volts through this coil to ground, kicking the points open, and rewinding the movement. This is an auto-rewind mechanism that keeps the clock wound as long as there’s 12-volt power.

09. Here’s the time adjustment shaft and gear cluster. The shaft is spring loaded into the disengaged position. Pull on the shaft (knob) against spring pressure, and the adjustment gear engages the time adjustment gear cluster, which moves the minute and hour hands mounted on inner and outer shafts and corresponding gears.

10. If you’re not concerned about originality and that periodic click sound, you can always opt for a quartz movement from any number of sources, including Instrument Services and National Parts Depot. For around $110, you can get into quartz movement and never have to sweat out electromechanical function again.

11. Clock hands can be removed with a small common flat-blade screwdriver or your fingernails. Be very gentle removing these hands. The second hand presses into an inner shaft that runs inside the minute and hour hand shafts for a total of three shafts.

12. The clock face is held in place by three tabs, which are gently bent open to free the face.

13. With the face removed, you can see how this classic ticker keeps time. It works like a conventional wind-up clock, with the difference being how it gets rewound. You can see the triple-shaft arrangement in front for second, minute, and hour hands.

14. The hour gear has been removed. The red gear is known as the motion wheel or gear, which transfers motion from the minute wheel to the hour wheel. Gear ratio through the motion wheel is what gets us hours versus minutes.

15. Here are the three gears that turn clock movement into hand position. From left to right are the hour gear, motion gear, and the minute gear. (Some call these gears while others call them wheels.)

16. There are two thrust washers on both sides of the minute gear. Instrument Services suggests removing these thrust washers when you reassemble with the quartz movement.

17. Assembly of the quartz movement begins with the minute gear. Again, do not reuse the two thrust washers.

18. Install the red motion gear included in the kit for the quartz movement next.

19. The hour gear is seated next along with the original wavy thrust washer. Don’t forget the small red time-adjustment gear, which is installed beneath the motion gear. This is what connects the time adjustment gear to the minute and hour hands.

20. New urethane mounts (gray) and washers have been installed. The clock and face are assembled together, as shown. Secure the clock face mount and movement with these tin clips, which are pressed onto the posts.

21. Install the clock face next, along with the hands. All you have to do with the face is bend the tabs over. When you install the hands, press the hour hand in place first, and set at either 12 or 3 o’clock. Install the minute hand at 12 o’clock. This synchs the hands. The second hand presses into the center shaft.

22. Reinstall the cover, as shown. Note the quartz clock movement ground tab, which grounds against the cover. A screw-on power post is installed last.

23. This exploded view provided by Instrument Services demonstrates how the quartz movement ties into the original clock gearing and face. Instrument Services provides clock repair, clock repair kits, and quartz-movement conversion kits.