Automotive Test Light with selectable 1amp and 500mA load.

A typical automotive test light win a LED draws very little current.  A standard test light with an incandescent bulb draws very little, typically about 250mA.

This test light uses two 10om resistors wired in series, with a switched center tap to create a load.  With an automotive 12 system,  these resistors will produce two selectable load options.  The exact load will depend on the exact output/charge state of your battery.

The calculated load would be 600mA and 1.2 amps, respectively.  Of course, actual draw will depend on the resistance in the wiring and the power consumption of the LED as well.   I built one and tested it with an Innova multimeter, the result was 980mA with the center tap switched on and 525mA with both resistors in series.   So, 500mA and 1 Amp is what I put on the label.

With the toggle switch “on” (closed circuit), the tester will bypass the 2nd resistor and draw 1 Amp.   With the switch “off” (open circuit), the tester will use both resistors in series and draw 500mA.

I included the step files, and a lid version with no engravings,  so you can change whatever you like.  

There is a bill of materials with Amazon links in the attached wiring diagram .pdf file.  Unfortunately, most of the parts required aren't available individually, so you'll have enough parts to build several of these.

You will need:

4 m3 heat set inserts

4 m3x8 socket head screws

2 m4x12mm socket head screws

2 10ohm 10watt ceramic resistors

1 mini spst toggle switch

1 2.5" trailer LED marker light