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VW Test Light – US 1115 Home Brew

So, I need to test my fuel and cold start system, but finding the VW US 1115 LED test tool is a bit hard. Not to mention it would cost more than it’s worth. Well, the Bentley details how to make your own, with cheap parts from your local electronics store. I decided to make mine a bit more interesting along the way. “Why don’t you just use a regular test light?” As it states in the Bentley, “Many of the electrical tests… require the use of a special LED test light, since the use of a more conventional test light with incandescent bulb can damage sensitive electronic circuits in the ignition, fuel injection, and emission control systems.”


  1. Solder Iron

  2. Dikes “wire snips”

  3. Wire strippers


  1. (1) LED

  2. (1) 1/4 watt, 330 ohm resistor

  3. (1) alligator clip test wire cut in half

  4. (optional) random small toy

The Basic Steps:

  1. Understand which side of the LED is (+) and which is (-). The (+) side is the longer lead. You can also tell by looking at the anode and cathode inside the lens. The anode (+) is the smaller / thinner metal piece. This is important because light emitting diodes are directional, as all diodes. Image compliments of Wikipedia:

  1. Solder the resistor to the negative side of the LED. (Resistors are non-directional.)

  2. Solder the test wires on each side. I used a red one for (+) and black for (-). So, I ended up cutting two test wires in half to make this.

Image from the MK2 Scirocco Bentley

There you go, you now have your safe test light made. But, my is it ever ugly. Take a look at the rest of the pictures below. You will see how I made my test light a bit more fun.

My quest for the coolest test tool starts with this small little toy from Dave and Busters.

Just for kicks, I’m adding pics of the resistor and LED packages I bought. A little shameless plug to the store.

And so dismantling starts. I start by using my torche to heat the glue and pull the toy apart.

Then, I start assembly. I cut a slot for a mouth and slide the LED in the slot.

Next, goes in the resistor and wires. Note the knot in the wire. This will prevent tug that can cause shorting or rip the connections out.

All coiled up and separated, ready for the hat to go back on.

The wires hanging out.

LED mouth.

All back together…

Hooray, it works! Lights on folks.

What will your’s be?

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