Many Chrysler Airflows were equipped with a hi-beam indicator in the headlight switch knob. Special wiring from the dimmer switch back to the light switch illuminated a small bulb in the switch that could be seen in a small lens in the center of the switch knob though the knob’s hollow shaft. Most of the Chryslers I’ve seen, including my own 1937 C17, have lost the lens. Without the lens, it becomes impractical to view the hi-beam lamp: you need to lean over and look right down the hollow shaft to see it.
In a discussion on the Airflow Tech Forum, airflowcars.groups.io,one reader reported using optical fiber (FO) though the hollow switch shaft to transmit light from the indicator bulb up to the hole in the knob where it can be seen. Poking around on the Internet, I couldn’t find any small enough lenses, but I did locate a supplier in India who sold 4 mm red garnet jewels. With the help of these jewels, some 1.5 mm FO, a bit of acrylic filament for a 3D printer (2.88 mm diameter), and a tube of cyanoacrylate (fast-setting super glue), I was able to assemble a replacement lens with attached optical fiber. Besides gluing the pieces together, I placed a drop of glue on the optical fiber before sliding it through the hole in the knob to hold the assembly in place. The bit of glue that wiped the hole itself helped cement the lens to the knob.
To assemble the kit, my technical assistant and son-in-law Dr. Mark Rasmussen used a small soldering pencil to melt a depression into both ends of the 10 mm (3/8”)-long piece of 3D printer acrylic to provide more contact area for the conical-backed jewel, easing the gluing. We added that short piece of acrylic as an adapter because we believed the FO was too skinny for direct gluing to the lens. For the first prototype, which went into my C17, we drilled the FO end of the adapter with a 1.5 mm drill Mark had. This made a snug slip fit, but it was difficult to keep the drill in the center of the fiber. We glued the next one.
The FO light pipe needs to be trimmed to not protrude from the hollow knob shaft. I'm sorry I forgot to measure mine for this article, so unless you have a spare knob with shaft, you will need to remove yours from the switch. The knob shaft is held in place by means of a semi-flexible, vertical tab in the switch that engages a square cut vertical notch in the knob shaft. To remove it, in theory, you can turn the knob 1/4 turn in either direction. This will cause the shaft notch to lift the tab and reposition it to a rounded portion of the shaft free of the notch, and the shaft should slide right out.
After installing and trimming the lens assembly into the shaft, reinstall it. On the switch end of the shaft, two parallel flats are ground at right angles to the retaining notch. To install the knob, therefore, (assuming your switch is installed right side up, that is, with the bulb socket on the bottom) rotate the knob a quarter turn to the right or left so that the “HEAD” marking on the knob is at 3 or 9 o-clock, and the flats on the end of the shaft are vertical. Slide the shaft into the switch. The flats on the end of the shaft (now vertical) should slide past the retaining tab and then stop when the tab encounters the shoulder. Now rotate the knob a quarter turn so that HEAD is at the top. The flats on the end of the shaft should lift the retaining tab in the switch so the knob and shaft can be slid home where the retaining tab snaps into the notch.
I say “in theory”, because on mine, the retaining tab was sticky, and the described removal method didn’t work with the limited torque I was willing to apply to the knob. I had to reach up the back of the dash to the switch and move the tab toward the right side of the car to get it to release. Similarly, it did not snap by itself into the retaining notch in the shaft. But a light touch caused it to engage securely.
Parts I used:
The jewels came from Etsy.com and were called "10 pieces 4mm Red Garnet Faceted Round Gemstone". The cost was $17 plus $3 shipping, which took about 3 weeks. Take care that what you buy is 4mm diameter and does not have a mirrored or opaque back. Some craft jewels do not pass light.
Mark already had some fiber optic, but I just found some on eBay here . eBay offerings vary, but if this one is gone by now, you want 1.5 mm optical fiber and you don't want 10 miles of it. End glow is best, and you'll need maybe 3 inches. The eBay ad above was about $5 for 100 feet. Hobby Lobby maybe? Radio Shack?
The adapter we rigged up we stole off his 3D printer. You want clear acrylic or optical fiber, diameter 2.5 to 3.0mm should work. Look for clear, 2.88mm 3D printer filament. Possibly, if your FO is very straight, you might be able to glue the jewel to the knob hole and just poke the FO through the knob shaft until it hits the jewel. Then glue it in place. We didn't try that.
For glue, what worked for us was a fresh, runny, super glue. Here's one: Bob Smith Industries BSI-131H Insta-Cure Thin Super Glue, that claims to be runny and dries really fast. After fiddling with the first prototype. Mark remembered he had some accelerant that made it set instantly and work much better. Something like this, Akfix 705 Accelerator Spray [Activator] for CA - Super Glues.