Arduino / Raspberry Pi based instrumentation?

Hi all,

So I recently ordered a Raspberry Pi and more associated small equipment to make myself a NMEA wireless bridge/repeater. The plan is to (based on a recent Panbo article) utilize a Win8.1 cheapo tablet to run OpenCPN. I've already run the instrumentation and had it all working on my laptop at the helm, and even had OpenCPN acting as a TCP server....so this is no challenge.

*HOWEVER*, this project got me thinking. My Yanmar 3ym30 has only the idiot lights for water temperature, voltage, and oil pressure. At various stages, I've thought about upgrading the Yanmar Panel ($1000+ all in), buying the Maretron N2k instrument andharness ($700 all in), and the cheapest option, splicing in to the existing wiring and putting in analogy instrument gauges.

Then, I thought, hey, I have the raspberry pi. Why not use an arduino board to tap this data this way!?

The trouble is, I'm not very well versed with arduino and instrumentation. However, if I'm willing and able to fund the hardware purchase(s), is there anyone that can guide me through the project? The best thread I've got is this as a reference: Boat Digital Guage Project - Arduino Forum

I figure I'd start with a simple question...so here goes:

Q1 - can someone tap into existing idiot light gauges (at the sender or at the panel) in order to splice the data? How does one interpret the values being returned by the sender gauges (assuming they return various voltages or resistances back to the idiot lights helmide).