1993-1994 Mazda RX7s like previous RXs seem to develop problems unique to their generation e.g. early second Turbo 2s have vibrations in the drivetrain more specifically, imbalances associated with the transmission. Third gens. (93-94) RX7s are plagued with instrument (gauges) problems and speedometer- odometer issues are common. I am working on a automatic 94 rx7 that has a working speedometer but an odometer that recently stopped showing. There are some places here in Florida that claim to be able to  bring these units back to life. I made the decision to do some investigations including online threads to tackle the odometer issue. In this particular the engine check light was on  and flashed 6 times for speedsensor malfunction. First order was to replace speed sensor (after checking wiring) which sells for $271.0 from the mazda dealer, result; nothing changed. I removed instrument cluster which is quite a job to check speedometer- odometer itself. To my delight, there it was a burnt 1000uf Capacitor just what folks online  said I would find, I got the Capacitor online soldered in and also another Cap. of lesser value that’s been known to fail. The grand result was that the odometer worked! but only for a few minutes after starting the car. No codes came up from the computer though, but there must be other problems in the speedometer circuit board and my guess is that the culprit is probably a diode but which one. Ahhhh the saga continues…….  I will post anything else that I find provided that I sum up the courage to go back into the 94 RX7’s instrument cluster….what a job!