My 1994 toyota t100 4x4 automatic longbed check engine light went on first then the overdrive off light flickered intermittantly. Then I noticed speedometer and odometer stopped working.

I checked fuses, disconnected and reconnected the battery.  This stopped the
overdrive off light.  I was trying to trace the speedometer cable but eventually
was told my problem was the speed sensor I wanted to diagnose before buying
parts but none of the parts stores have the OBD1  (?) tool.  Not for sale or their
own use.  The tool that plugs into vehicle and comes up with a code for the
check engine light. I'm trying to avoid the dreaded mechanic labor fees.  I'm
sure I'll find the diagnostic tool eventually, but any suggestion on how to
proceed.  I did follow what I thought to be the Speedometer cable to the
transmission and found a crusty soft spot but auto part guy said I don't have a
cable it's a sensor... everyone has the "right answer"  for my problem but I'm
not willing to open a can of worms that I can't fix immediately especially since
the trucks running right now not so much when I start removing and buying
unecessay parts for this old truck based on someones surefire solution.  Thank
you in advance for your remedial suggestion or solution.