WHT Z06 Modifications: LED DRL and Tail Lights

I've done two C6 Corvette LED conversion projects, tail lights in 2009 and daytime running lamps (DRL) in 2017.

Tail Lights

I've always thought the C6 should have been made with LED tail lights. Not only do they look cool but there's a subtle safety aspect to them. They turn on much faster. Incandescent bulbs require 200 ms to come up to brightness. Eliminating this delay means the driver following you can react to your brake lights 200 ms sooner. When you're doing 55 MPH, that's sixteen feet!

There are a number of aftermarket C6 conversions out there but most of them look cheap to me. With a price range of $500 to $2100 they are are anything but. What I really wanted was factory appearance with LED internals.

I learned that Pratt & Miller uses LED tail in their C6R race and C6RS street cars; further investigation revealed they use LED tail light modules first seen on the 2006 Mercury Mountaineer. These are glued into the stock C6 Corvette tail light reflector assemblies.

The LED modules are made by Sylvania/OSRAM and are part of their Joule LED lighting system. This clever design places surface mount LEDs in a heat sink assembly outside of the tail light assembly. A clear plastic tube carries the light up to a mirror that shines it on the tail light reflector. Keeping the LEDs outside of the tail light is an important feature because LED light output is sensitive to ambient temperature.

There are two Joule LED module part numbers that were widely used. The 2006 Mercury Mountaineer uses L1224R-01 (Ford 6L9Z-13B765-AA) and the 2008-2012 Chevrolet Malibu LTZ uses L1230R-02 (GM 25874489). The focal lengths are encoded in the part number and are 24 and 30 mm while the focal length of the incandescent light socket in the C6 Corvette tail light is 29.45 mm. In an attempt to maintain the correct focal length, I used L1230R-02 modules. A drawback to this choice is that the L1230R-02 uses a 4-pin USCAR connector which is difficult to obtain.

Mounting

I wanted this modification to be reversible so gluing the modules in wasn't an option. I first considered making an adapater that the LED module would lock into and in turn lock into the tail light assembly. However, the geometry of the LED module's locking lugs and those on the C6 tail light socket make this design difficult to fabricate. Also, two weather seals instead of one would be needed and this would impact the focal length.

My solution was to make adapters that would mate with the C6 tail light and epoxy them to the LED modules. To make the mold master, I cut up a spare C6 tail light socket and glued a spacer to it. Next I made a mold using Alumilite QuickSet RTV silicone and cast a number of adapters using Alumilite Regular urethane resin.

Mold making preparation

The end product is surprisingly durable and can resist temperatures up to 250° F. It takes 4-8 hours for the silicone to cure but only 4-8 minutes for the resin to set so once the mold was completed it only I was able to quickly make all of the parts. Once the adapters were ready all that was left was to trim the lugs off the LED modules and epoxy the parts together with J-B Weld.

Final module assembly	Locked into tail light

I notched the adapter to make it easy to maintain connector orientation when gluing. After applying a little dielectric grease, I reused the weather seals from the incandescent light sockets.

Load Resistors

A common problem with LED conversions is that the turn signal and emergency flashers blink too fast. A flasher is basically a coil wrapped around a bimetallic strip. When you apply current the coil heats the strip causing it to flex and break the circuit. As the strip cools, it straightens and completes the circuit.

LEDs draw less current than the incandescent bulbs they replace. This means the bimetalic strip doesn't heat up as much. Since it takes less time to cool down the flasher cycles faster. Adding resistors simulates the load of the incandescent lamp and causes the flasher to cycle at the original rate.

The C6 Corvette uses a 3057LL double filament wedge lamp in all four of the rear tail light assemblies. The primary filament is rated at 2.1 A @ 12.8 V. The pair on each side are wired in parallel when you do not have RPO T79 (rear fog lights). The LED modules are rated at 3.5 W @ 13.5 V which is 259 mA. If we add up the current from the two incandescent bulbs and subtract the current from the two LED modules we find that we'd like each load resistor to draw about 3.7 A @ 12.8 V. This means we can use 3.5 Ω, 50 W power resistors.

Wiring harness

Rather than hack up my wiring harness, I made a short adapter and inserted it at connector C455 which is located behind the right tail lamp assembly. This is the junction that connects the I/P harness to the deck lid harness and it provided access to all of the relevant tail light circuits; here's the pinout of connector (Rear body harness to I/P harness).

Pin	Wire color	Function
A	BK	Ground
B	L-BU	Stop lamp supply voltage
C	L-GN	Backup lamp supply voltage
D	YE	Left rear stop/turn lamp supply voltage
E	BN	Park lamp supply voltage
F	TN	Rear compartment lock actuator unlock
G	D-GN	Right rear stop/turn lamp supply voltage
H	OG	Rear fog lamp supply voltage (T79)

Note that RPO T79 is the export option for rear tail fog lights and so pin H is not used for domestic applications.

I attached the load resistors to a piece of 1/8" aluminum and mounted that under a ground on the right side bumper. I used a 3-pin Delphi connector to make it possible to disconnect the resistors and use the incandescent bulbs without having to remove my wiring harness.

The resistors are wired between ground (pin A) and the left (pin D) and right (pin G) tail/stop and turn signal circuits.

The 8-pin Delphi connectors are readily available but the 4-pin USCAR connectors are not. In the end I lucked out and found someone who had four. As more cars use these modules the connectors should become a commodity item. After I finished splicing the wires together I wrapped it in Elliott Tape ET-301 dry vinyl wiring harness tape which gave it a totally factory appearance.

Here's a parts list for the wiring harness:

Quanity	Delphi	Mouser	Description
1	15326840	829-15326840	GT 150 8-way connetor (male)
1	15326835	829-15326835	GT 150 8-way connetor (female)
1	15326813	829-15326813	GT 150 3-way connetor (male)
1	13519047	829-13519047	GT 150 3-way connetor (female)
10	15326269	829-15326269	GT 150 terminal (male)
10	12191819	829-12191819	GT 150 terminal (female)
20	15366060	829-15366060	GT 150 cable seal (blue)
2	15305171	829-15305171	GT 150 cavity plug (green)
2		71-RH50-3.5	Power Resistors 50 W 3.5 Ω 1%

Notes

• The fourth pin on the L1230R-02 module is used for outage detection.

• Here's a current list Joule LED modules and the applications they are found in:

OSRAM	OEM	Application
L1224R-01	6L9Z-13B765-AA	2006-2007	Mercury Mountaineer
L1224R-01	8F9Z-13B765-A	2008-2010	Mercury Mountaineer
L1230R-02	25874489	2008-2012	Chevrolet Malibu LTZ
L1224R-01	8F9Z-13B765-A	2008-2009	Ford Taurus X
L1224R-01	8F9Z-13B765-A	2008-2009	Mercury Sable
L3230R-3N	AR3Z-13B765-A	2010-2012	Ford Mustang

• The 3057LL outputs 32/2 MSCD (402/25 lm). The Joule module outputs 47/3.5 lm (@ 12.8 V). The reason the LED module is brighter is because it only outputs SAE red.

• The LED tail light brightness is supposed to be 10% of the stop light brightness. The lower light output is achieved using pulse width modulation. The specs say it is a 5.7% duty cycle at 240 Hz however I measured it to be more like 255 Hz with an oscilloscope:

  PWM waveform	PWM detail

• The male USCAR connectors used on the Joule LED modules are 064-S-003-1-A01 (3-pin) and 064-S-004-1-A02 (4-pin).

Daytime Running Lamps

The stock C6 Corvette daytime running and turn signal lamps are also incandescent so of course I wanted to upgrade them to LED.

Sylvania has two lines of automotive LED lamps. The first is the 4157A (4157ASL.BP2) which is a cylinder with 18 surface mount LEDs. These approximate the stock lamp output but I found the dim (marker light) brightness to appear dimmer than a stock 4157NA lamp.

Sylvania 4157A

The other option is the Sylvania Zevo 4157A (4157ALED.BP2). The dim circuit is perfect and the bright is brighter but only when looking from directly inline and looks good off-angle. These are what I used.

Sylvania Zevo 4157A	Installed in DRL connector

Load Resistors

The stock DRL/turn signal lamp on a C6 Corvette is the 4157NA. There are two elements and the primary is rated 2.2 A @ 12.8 V, uses 28.5 W and outputs 302 lumen. Using a 6 Ω, 50 W power resistor gives us 25.6 W. The Sylvania Zevo is rated at 1.5 W @ 13.8 V which gives us 27.1 W.

Wiring harness

As with the tail lights mod I made two wiring harnesses to add a load resistor to each side. There is one connector for each side. C119 is the left and C120 is the right but the pinout is basically the same.

Pin	Wire color	Function
A	BK	Ground
B	YE	Headlamp Low Beam
C	D-GN/WH	Headlamp High Beam Supply Voltage
D	L-BU/WH	Front Turn Signal Lamp Supply Voltage
E	BN	Park lamp supply voltage

All of the circuits are passed through with the resistors wired between ground (pin A) and the turn signal supply voltage (pin D) circuits. I mounted each resistor to a aluminum plate for mounting.

Each harness is inserted at C119 or C120 and the resistor plate is attached to a stud that hangs off of the HID module using a M6-1.0 nut.

Sylvania 4157A

Here's a parts list for the wiring harness:

Quanity	Delphi	Mouser	Description
2	15326647	829-15326647	GT 280 5-way connector (male)
2	15326642	829-15326642	GT 280 5-way connector (female)
6	15304731	829-15304731	GT 280 terminal (20AWG male)
4	15304732	829-15304732	GT 280 terminal (14AWG male)
6	15304719	829-15304719	GT 280 terminal (20AWG female)
4	15304720	829-15304720	GT 280 terminal (14AWG female)
12	15366065	829-15366065	GT 280 cable seal (orange)
8	15366067	829-15366067	GT 280 cable seal (tan)
2	15430895	829-15430895	GT 280 Secondary TPA (5 way)
4	15317832	829-15317832	GT 280 CPA lock
2		71-RH50-6.0	Power Resistors 50 W 6 Ω 1%

Notes

• GearWrench (formerly K-D Tools) 3888D push pin pliers can be helping for removing the plastic body clips from the fender liner and front light assembly cover.

• I used 14AWG wire for the A and B circuits and 20AWG for the others. This is because the HID lamps are rated at 55 W but can draw well over 100 W on statup while the H9 incandescent high beam uses 64 W.

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Craig Leres