OBD II diagnostic tool recommendations?

[robselina]

I've had some bitchy electrical problem on the wife's grand cherokee for over a year. I've taken it to a couple different mechanics who've had their fun with it, replaced almost my entire electrical system (literally) and I still have the problem.

At this point, I've decided I'm dealing with it (I know, should have just done this to start with). I want a good diagnostic tool to see what the hell is going on with my engine. I don't want something that will just read off engine codes (it doesn't throw any), I'd like to be able to see individual sensor output, etc. I do have a laptop BTW.

Anyway, I'm looking for some advice on a relatively afordable system to debug my electrical issues. Any advice?

EDIT : Vehicle is a 1995 Jeep Grand Cherokee with the 318 (pre-OBD II)