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
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.