This article was originally written as a post to the gm-volt.com
forum. It is both a description of what I did, and a tutorial to
show others how to do the same thing. Although I re-wrote
portions of the article, there are still some of the sections where I
am clearly instructing others how to do it.
recently replaced my front turn signal / running lights on the Volt
with switchback LED bulbs. I had to look up "switchbacks" when I first
heard the term. They are a form of a combined running light/turn
signal LED bulb with built in logic. The logic turns off the
running light when the turn light is flashing. There are two
types of this logic. The simpler merely turns off the running
light during the time the turn light is on. The result is that
during a turn the light is alternating between white (running) and
amber (turn). The other logic form turns off the running light
during the entire period of time the turn is flashing. This
results in the light being dark between flashes of the turn.
light bulbs on modern cars is nothing like in the old days! You
used to be able to reach behind the bulb, twist the socket out of its
mount, change the light bulb, and be done in a minute or so. Now
the bulbs are buried deep withing the structure of the car and bulbs
are usually considered a dealer task to change them, often requiring
body parts to be removed for access.
There are a number of
threads on the GM-Volt forum describing changing the front turn/running
bulbs, which basically describe two techniques. The driver's side is
not bad for access, but the passenger's side has the charger in the
way, and you have to make enough room to work around it. The first of
the two primary methods I have seen are to pull the screws holding the
fender liner then disconnect the right side of the bumper and pull it
forward. The other is to have an assistant hold the fender liner after
the screws have been removed, then work one handed in the limited space
available. As I am basically lazy, and I don't have easy access to an
assistant, I figured there must be an easier way.
are two problems to solve: 1. Get access to change the bulb. and 2.
Install the load resistors to prevent hyperflashing. Hyperflashing is
the rapid blinking of a turn signal when a bulb is burned out. It
is required by federal regulations. The flashing circuit senses
the load of the bulbs, and if it is too low, hyperflashing results.
As the LED bulbs draw much less current than incandescents, they
will hyperflash if the load is not built back up the the old level.
Resistors are used for this, usually 6 ohm 50 watt.
change the bulb, I pulled the fender liner screws and several screws
holding the short air dam to be able to move the area just under the
bulb about 1/2 inch. I made a tool from a length of 3/4 PVC pipe with a
slot in the end just over 5/8 wide and about 1 1/4 inches long. Using
this tool I went up from under the car, (which I had driven up on
blocks) and pressed the slot of the tool over the end of the light
socket. It was then easy to twist the tool to remove the light and its
socket from the car and let it drop down through the opening behind the
On the left you can see the tool on the light socket. The right shows the socket hanging down and the LED bulb installed.
had some trouble trying to reverse the operation, as the tension of the
wire kept pulling the socket out of alignment. I then removed the
socket from the harness (it is attached with a connector), used the tool to replace the bulb and socket
into the housing, then I used the tool to plug the harness back into
the socket without any problem. I replaced a few screws and the
passenger side was done!
A word of caution: Be sure and try the
light before replacing it in the housing. These bulbs are polarity
sensitive and will only work in one orientation. If it doesn't light,
turn it around in the socket.
The bulbs I used are from Super
Bright LEDs. I used them since I know they make great products, they
have the correct type of bulb for our vertical orientation (no lens
pointing up), they are relatively short for our limited space, and
their bulbs totally blank the white light while the amber is flashing.
Some brands alternate white and amber while flashing and don't show up
nearly as well.
This is how the new bulb looks on the passenger side.
the resistors: The wires for both sides of these lights pass through a
connector on the Driver's side. Since there is much better access on
this side, I decided to locate both resistors there.
engineer, always an engineer! I was worried about the temperatures the
resistors might reach under sustained use of either the turn signals,
or more likely for long periods of the emergency flashers, so I did
some experimenting. I mounted the resistors on a heat sink I had. It
was 4 1/2 by 4 3/4 with lots of fins. I hooked one of the resistors to
a 10 volt supply which simulated 50% power like a flashing light would
average. I recorded the temperature at intervals up to 15 minutes and
plotted them. I then did the same for the resistor mounted to the
heatsink using thermal compound. I then tried it with the resistor
hanging in air with no heatsink as the vendors often tell you to do.
After pulling the driver's side fender liner back and checking out my
actual available space, I made a heatsink of 3/16 aluminum about 3 3/8
square, I also ran a temperature graph of this.
you can see below, the resistor really gets hot hanging in mid air, but
any of the heatsink combinations keep it relatively cool.
comments please about the fact that I only energized one resistor. I
know it will get hotter with both energized during emergency flasher
operation, but my test was really to show if a heat sink would make
much difference, and it obviously does.
I discovered when
working on the driver's side that I actually had more room to work with
the wheels turned to the left. When they are turned to the right the
tire limits how far you can move the liner. Of course removing the tire
would give you the best of both worlds, but as I said, I am lazy.
decided to mount this smaller heatsink on the metal structure just
above the horn. There is adequate clearance from any other parts to
avoid any damage from the heat - even though it is much lower in
temperature, it is still hot!
then had to tap into the harness
coming from the 6 pin connector. On my MY2013, the right turn was a
light green/violet wire, the left turn light blue/white, and the
ground, black. I opted for Posi-taps, which are expensive, hard
find, and reliable! They make one that is rated for the approximately
20 ga wire used in this location. These worked well, and in my
opinion are much more reliable than the typical red Scotch-locks we all
shows the taps into the harness wires on the left, and the cleaned up
version on the right, which also shows the mounted resistors.
am very pleased with the final results: The switchbacks give a
little extra close illumination at night and are a little more
distinctive when showing a turn signal, but most importantly, they look