• By
  • On 5th April 2015

Don’t make the mistake I made in thinking that you can buy a couple of vintage taillights, put new dual-filament light bulbs in them and they’ll fit perfectly. They won’t. And don’t make the mistake I made assuming that all lenses are the same “standard” size. They aren’t. Equipping your custom bike with custom “period looking” taillights is an education in electricity, size standardization (or lack thereof), and “rat tails” (yes, that’s what they call the braided cord that goes around the wires).

You can, of course, buy brand new Made in China taillights and call it a day. They come in all varieties of style and finish. You can even buy the “VINCENT HRD” style that have the word “STOP” cut out in the chromed retaining clip. They are ready to install and cost significantly less than what you’ll end up spending if you really wanted to make your own.

All authentic vintage taillights used 6V single-filament light bulbs. These have a single electrical terminal at the bottom. Correspondingly, the original light bulb socket has a single terminal as well. The 6V light bulbs have two locking pins at the same level. Modern dual-filament 12V light bulbs have two terminals at the bottom and staggered pins (so they can only be installed in a specific way; you don’t want the light to dim when you apply the brakes).

Lesson #1: A vintage tail light’s original socket cannot be used with modern light bulbs.

The original socket needs to be replaced with a new one, which is made to accommodate a 12V dual-filament light bulb and has cut outs for staggered pins. That’s fairly easy to do. Grind the end of the old socket off, put the new one in, bend the tabs and that’s about all that needs to be done.

Then you buy a dual-filament light bulb from your local auto parts store, install it into the new socket, connect it to a battery and it lights up! Now you are ready to complete the assembly by installing the original vintage glass domed lens. As you do this, you discover that the lens cannot reach the taillight’s housing because it bumped against the new light bulb. What the…!

Lesson #2: New light bulbs are much bigger than vintage light bulbs.

Light bulbs compared

The original 6V light bulbs were about 1 and 3/8” long. The modern dual-filament light bulbs are about 2” long. Since the glass domed lenses made back then were 1 and ½” high, there was plenty enough room for a good fit with the old 6V bulb. But the lens cannot be fitted to the housing if modern light bulbs are used.

Light bulb and lens heights

What now?

Fortunately, there is a demand for such dual-filament “low profile” light bulbs by vintage car aficionados who collect, restore and drive beautiful old cars like Ford A, Ford T and others. If there is a demand, somebody always responds to it and as a result you can buy such “low profile” dual-filament light bulbs today form places like Snyder’s Antique Auto. They also sell the sockets.

OK. You got your new sockets, new “low profile” light bulbs and everything fits perfectly. Now, all of a sudden, the old glass (or plastic) lens doesn’t look good anymore. Everything else is new and you must replace the cracked old glass lens or you simply want a different color (a deeper ruby red perhaps?). You buy that very rare glass lens from the 1930’s, unused and its original box, that looks absolutely perfect and for which you paid through the nose by bidding-to-win on eBay. You can’t wait to see what it’s going to look like once illuminated by your new and better light bulbs. It’s going to look gorgeous. You know that. You install it and… it doesn’t quite fit! It’s just a hair too big; instead of 2 and ¾” diameter you need the lens is 2 and 7/8”. Damn!

Lesson #3: Glass lenses of the old days came in many different sizes. Many are not interchangeable.

In trying to get a “perfect” pair of taillights, I ended up assembling a small collection of various different housings, lenses and visors. Two of them were an exact match. I then bought a pair of new old stock Lucas lenses that fit perfectly, made my own brass visors and the result was this: