After my alternator died last month, I decided to search for a voltage gauge which would not be too obtrusive in the passenger compartment...Who wants to look like a ricer, right?
I stumbled upon a 12v "cigarette plug" digital voltmeter on ebay for less than $20 shipped. I wasnt sure, but it looked as though I could take it apart and sink it into one of the blank switch locations in the dash.
I was right! It's as if it was made specifically for a Boxster!
Here is what I bought:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270333726819&sspagename=STRK%3AMEWNX%3AIT&viewitem=
I took it apart, connected longer wires and hooked up the positive to an ignition source (I used the radio), and grounded the black wire to a cig plug. I used a little bit of clear silicone RTV to seal it into place (from the back side, of course).
You might also notice a couple other mods in the pics. I added another cigarette plug to the blank location, and 2 OEM garage switches (one for my garage door opener, the other for the gate). I soldered wires to the openers and connected them to the switches. The "clickers" are stuffed back behind the dash panel. You can't see it from this picture, because I didn't have the headlights on, but the garage switches and cig plug surround all light up at night. I ran wires across to the other side and tapped into the existing switches.