LEDS for Instrument Cluster and VDOs - New Thread

LEDs are a great way to eliminate the need to be continuously replacing
lightbulbs in the gages and instrument panels of automobiles. The reasons
are (unlike incandescent filament bulbs), they last almost indefinitely,
they draw significantly less current, and they don't get hot. As many of you
know, gaining access to these bulbs is not always easy (usually requires
some disassembly), so replacing the incandescents with LEDs will eliminate a
lot of repetitive and difficult work.

I own a 1988 VW (Rabbit) Cabriolet Convertible. This automobile has an
instrument cluster consisting of a speedometer, tachometer, digital clock,
fuel quantity gage, coolant temperature gage, and various LEDs acting as
"idiot" lights for various purposes. The instrument cluster is lit up at
night by a set of incandescent bulbs mounted on twist-lock sockets. The
printed circuit board of the instrument cluster provides the electrical
connection when the twist-lock bulbs are inserted into the bulb access holes
in the circuit board and twist-locked into place. There are no wires to
attach.

The other locations that calls for LEDs are the three VDO gauges in the
center console. Access to the bulbs lighting up each of these gauges is not
as difficult as gaining access to the instrument cluster, but it is still a
pain if you have to do it repeatedly, and you will when incandescent bulbs
are used. They burn out far too frequently.

So I began a search for a good LED that would work in both the instrument
cluster and in the VDO gauges. My goal was to find an LED that would light
up the instruments and gauges at least as well as the incandescents, and
require little, if any, modification to the instrument cluster or the VDO
gauges.

I found a good candidate at www.superbrightleds.com. It is an LED called a
T1.5-W, and it is a white LED with a black twist-lock socket. The price is
$1.79 each plus $5.00 for shipping. The T1.5-W has a built-in resistor, so
it is "plug and play" for automotive use.

This bulb is excellent in it's illuminating power, every bit as bright as
the stock incandescents, and will work unmodified in the instrument cluster.

However, a modification of the T1.5-W is necessary before they will work in
the VDO gauges. The problem with using them in the VDO gauges is that the
VDO gauges supply power to the bulbs OUTSIDE of the gauge cases, using the
gauge wiring harness to plug into a pair of male connections on each of the
stock VDO incandescent bulb sockets. So, since the T1.5-W twist-lock sockets
are designed to pick up power from the surface of a printed circuit board, a
modification was made. Here is what I did:

I carefully (warning: don't break the leads) pulled the T1.5-W LED bulb out
of the black twist-lock socket, then drilled a hole down through the length
of the socket (about 5/32 inch drill bit). This action destroyed the metal
pieces inside the socket - those pieces needed to be removed anyway to
prevent any shorts. Then I straightened out the 2 bare leads of the bulb,
pushed the bulb back into the socket as far as it would go, leaving a snug
fit. The white plastic divider of the bulb prevents the 2 leads from
touching each other inside the twist-lock socket.

This left about 1/4 inch of exposed leads out the back, which is plenty of
lead to work with. So I then soldered a 4 inch piece of insulated copper
wire (very small gage) to each of the exposed leads, and tested the bulb to
make sure it was still ok. A 4 inch set of leads should be adequate for
connecting to the wiring harness inside the center console. If not, I'll
just splice in more insulated wire.

End result. My VDO gauge faces are very well lit and nothing (no cutting or
anything else) had to be done to the VDO gauges or the VDO gauge cases.
Illumination of the gauges is outstanding. For the instrument cluster, just
remove the incandescent bulbs and replace with unmodified T1.4-W LEDs.

I did this with some spare VDOs at my workbench. It looks like the dimming
function will work when I put the T1.5 LEDs into my VDO gauges and
instrument cluster in my car. I performed a test at my workbench using a 9v
battery. In this case illumination seemed to be about the same. Then I used
three 1.5 v batteries in tandem (4.5 v total), and illumination was about 50
percent. Finally I used just one 1.5 v battery and the LED would not light
up.

I hope this write-up will be of benefit to some of you.

Regards.

One correction: The hole drilled through the length of the twist-lock socket
should be 1/4 inch diameter rather than 5/32. The larger hole provides room
for heat-shrink tubing around each lead (for better insulation). Make sure
the drill bit is centered to prevent drilling through the wall of the
socket.