Bulb holder for MBZ W114/W115 second series

These are replacement bulb holder assemblies for my 1974 Mercedes-Benz W115 230.4, second series with the ribbed tail lights.  The car has been unsafe to drive for several years because of unreliable brake/tail/turn lights, caused by deterioration (corrosion) of the sockets and the circuit traces in the bulb holders.  After many unsuccessful attempts to clean and repair the original parts, sourcing several used tail lights that were no better than what I had, and a failure to find new bulb holders or new tail light assemblies, I sat down and created my own solution.

These are designed around a bi-pin G4 bulb socket and a cylindrical G4 12V LED bulb. The bulbs and sockets are not intended for automotive use, this is not DOT/MOT/TUV approved. The choice of bulb and socket came about because I was unable to find a BA15S socket, or any other readily available automotive socket, that would fit in the tail light assemblies.  There is a distinct possibility of the bulb vibrating loose in use and causing a light to be out without the use of an adhesive, a band of heat shrink tubing, or both to help hold the bulb in place. I intend to use both. Check the specs for the specific bulbs you use, some are lower output than the original incandescent which is undesirable. I included pictures from the Amazon pages of the specific items I used to assist in finding the correct parts as well as the search terms I used, in case the links die or someone wants to source parts from other suppliers. Bulb test photos were done using an adjustable bench power supply at 13.8VDC, though I noticed no appreciable difference in light output from 11V to 14.6V.  While the bulbs I have don't care about polarity, some LED bulbs have a distinct + and - pin, so if yours don't work at first, take the bulb out and rotate it 180 degrees.

In addition to the bulbs, bulb sockets and whatever you choose to secure the bulbs to the sockets, you'll need ten M4x20mm or #8-32x3/4" pan head machine screws to use as pins for the harness connector, sixteen M2.9x13mm or #4x1/2" pan head sheet metal screws to attach the sockets  to the printed part, and at least a dozen ring terminals to connect the bulb socket pigtail leads to the machine screw "pins", along with heat shrink tubing and possibly a small bit of extra wire to lengthen the pigtail of one socket per side , since mine weren't quite long enough.

The models are labeled L and R for sided-ness and the pins are labeled to the best of my ability. My bulb holders had five sockets, but the reflectors and lenses only had provisions for four bulbs (brake, tail, reverse and direction indicator) and I have no idea what the fifth socket is for, possibly rear fog lights.  Because of this, there is one pin location unlabeled and I also left out the fifth socket location.  

Print in an appropriate filament, which is NOT PLA for this application.  Mine were printed with Overture PETG (black because that's what I had), but ABS, ASA and PA-CF/PA-GF should also be fine.

Bulb socket used: https://www.amazon.com/dp/B00U0R8AGO
search terms, in case the link dies or to find elsewhere "g4 socket" 

Bulb used: https://www.amazon.com/dp/B0GCM4JK2F
search terms, in case the link dies or to find elsewhere "g4 led bulb 12v 4w 480lm"

Using LED's for the turn indicators like this gives a "fast flash" when using the original flasher relay box.  And as currently designed, there is no connection on the LH bulb holder for the number plate light harness.  I'll be addressing both in the future, but for now I'm just going to live with it as-is and enjoy driving the car.