Heya my KB fellas

Im thinking of buying aftermarket tacho for my RF. And I has some questions. My RF has been rebuild with a uber weight reducing "tacho" made out of foam which has 3 guages with individual cables, (+,-,Ground) similar to these cables:

http://images.superchevy.com/technic...connection.jpg

Now, if you look at the new tachos etc you will see a psi port looking like so:
http://www.trademe.co.nz/Trade-Me-Mo...-168104744.htm

Question: where, how, why, how much.

OK, first of all what is the diffrence and is it practical (possible) to convert from one to the other.

Who will be able to help with a good selection of tachos

Is it better to fry one self (well... Im not that bad at electronics but is it reasonable for me, with knowlege of 555 chips, and trasistorsors to have a go at this) or better ask an electritian

If it is, whats the best way.

Pretty much a crash course in tachos all together. I know that there are mechanical ones, electrical and cpu chipped ones but what should I go for and what are the advantages. Il post the picture of my tacho asap.

Thanks