QUAD BRAKE LIGHTS FOR THE 300C
Since their introduction I noticed that only the top/round portion of the 300C’s taillights were used for the brake lights while both the top/round and bottom/rectangular portions were used for parking lights. Then the other day I noticed that the bulb in the bottom/rectangular portion actually had the minor and major filaments as in the top/round portion. So I thought I’d take a look into what it would take to get brake light power to the major filament of the bottom/rectangular portion’s bulb, and in the process yield quad brake lights.
To see how I did it, read on.
After opening the trunk, I located and removed the plastic wingnuts (one each side) that retain the interior trunk paneling.
Then I pulled the paneling forward to expose the electrical connector, slid the locking key, pulled the plug, and removed the wingnuts (two each side) next to and above the socket.
I then removed the taillight assembly by pulling it straight back and off of the fender, and took it to
the workbench to modify the wiring.
I found that the green socket at the bottom inside of the taillight assembly needed to be modified to add a third wire to bring brake light power into the socket so as to energize the major filament.
First, I cut the Black/Gray and White/Violet wires coming out of the green socket about 2” from the socket (I’ll explain why this is necessary later). Second, I removed the socket from the taillight assembly, and removed the bulb for safekeeping. Third, I stripped the four ends created by cutting the two wires about 3/8”, and twisted the bare wire ends.
After careful inspection of the contacts within the socket, and those on the 3057 bulb, I determined that there is a metallic tab within the socket in a position to contact the bulb’s base at the major element’s contact location. This position in the socket is located 9/16” in from the side and 3/4" below the top of the socket’s rim, as labeled in the picture.
To gain access to this metallic tab I first carefully drilled a 3/32” pilot hole just through the plastic until the drill bit bumped into the metallic tab within. Then I upsized the hole to 1/4", all the while being careful not to allow the drill bit to be suddenly pulled into the socket and wiping out the metallic tab in the process! As required, I removed plastic from the edges of the hole to fill out its full diameter with an Exacto knife. I then applied a bit of solder flux to the metallic tab, followed by a dab of solder (as pictured). I applied just enough heat to get the solder to stick to the metallic tab and not melt the plastic that retains the metallic tab.
Next I prepared a 12” long piece of hookup wire to be soldered into the hole of the socket by striping 1/4” of one end, tinning it with solder, and bending the end in two reverse 90-degree bends (as pictured).
I then trimmed the end of the soldered area back to about 3/16” to allow the end of the wire to enter the hole in the back of the green socket. After positioning the end of the wire in the hole I carefully positioned the soldering gun tip to the joint and applied sufficient heat to melt the solder on the wire to the solder on the metallic tab.
The bulb was then re-installed in the socket and the socket/bulb assembly re-installed into the taillight assembly.
Now for the explanation as to why the Black/Gray and White/Violet wires were cut earlier in the instructions. While doing so eases the operations of drilling the hole and soldering in the third wire, this is not why they needed to be cut. I discovered the necessity for this while pre-testing the operation of the newly wired major filament of the green socket’s bulb, which didn’t work exactly right! After further study I determined that the internal connections of the green socket (which was intended for minor filament operation only) needed to be cut in order to flip their connections so as to reverse the ground and minor filament power sources within the socket. This moved the ground wire to the ground connection point of the major filament of the bulb, and all was well.
So, I spliced the Black/Gray and White/Violet wires in the flipped configuration as pictured to achieve the required results.
Next, I extended the third wire from the green socket up to the black socket of the brake/park bulb, and spliced it into the Dark Green/White wire. I soldered the connection (as picture below) and taped the joint.
Then I went back to the green socket and applied a dab of silicon adhesive/sealant to the hole to seal up the wire entrance into the socket as pictured below.
The finished product should look like this from the inside ………………….
……………….and like this from the outside when re-installed on the car:
For those who would like a .doc or .pdf version of this information drop me a PM with your e-mail address indicating which (.doc or .pdf), and I'll send it off to you.