Diagnostic Code Reader ('95 & Earlier Troopers)

The Stately Eggcrate is a 1990 5speed 4door 4wd Trooper with 2.8Liter V6. 190,000 miles is about to turn, but the Crate, among other things: is
meticulously maintained w/all 6 cylinders pressure-testing w/in 5 lbs. of each other; burns less than a gallon of Mobil-1 every +2000 miles; & is rust-free inside, outside & underneath w/the exception of a few small bubbles on right lower rear hatch door. LOVE this car: a) As a huge gear-totin', totally comfortable passage-making machine; b) As a speedy trooper-foozler (it looks like it's fustily putt-putting along at 65 mph when it's actually touching 80+); & c) With tires dropped to 8-10 psi, as a well-balanced, just right powered & geared mountain goat of a surf-fishing beach buggy. Goal: To keep the Crate goin' in apple-pie order fot snother 200,000 miles, without perpetual false "CHECK ENGINE" red dash alarm lights scaring the wits out of my better half. Query: Does any similarly situated Trooper fan out there in Isuzu-Land know of a company making after-market Diagnostic Code Readers for '95 and older Troopers? Old after-market parts stand-by JC Whitney/Chicago throws up its hands at the very mention of the question. The closest I've come so far is www.autotap.com, which offers software/hardware/cabling kits which they advertise enable users to diagnose their vehicle by using their desktop/laptop/Palm. Have any owners out there tried this solution, and, if so, with any joy?
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