Stumbled  across this on Fleabay Motors.  It's a voltmeter that you can plug into your car's cigarette lighter socket to check the battery voltage:

Thought something like that would be handy for checking the batteries on my K bikes but of course nobody makes one in a Powerlet plug version so I decided to make my own.

The body of it is one of these dual use plugs you can get on Fleabay for $1.98 shipped.  When you pull the red cap off of the tip it fits into a Powerlet socket.

(BTW: I don't recommend this type of plug.  I bought this to see if they were worthwhile.  It will work fine for this application but better ones can be had. There's a UK seller on FleaBay, AutoStar, that has some better ones for a reasonable price.)

Then I found this mini LED voltmeter that's powered by the voltage it's testing.  $1.38 shipped.

I drilled some small holes it the sides of the plug and used some fine brass wire to hold the LED in place on top of the plug.

Then I put the plug back together, wrapped some tape around the top of the body of it and filled that with five minute epoxy to "ruggedize" it.  Here's the final product:

It's not particularly attractive but it works great and is much easier than using a multimeter to check the battery voltage.

© 2013 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.