My hold light on my 1990 Mazda 929s comes on. This is stopping the speedometer from working therefore the cruise control does not work. This hold light is the one on the dash where you can tell what gear the car is in. It says hold and it is blinking constantly.

Take it to the dealer and have them pull the code(s) on the transmission. There's a different code reader than the engine reader.

Stop, before you take it to a dealer. Trace the speedo cable to where it goes into the transmission. make sure the cable is still connected, also unscrew the 13mm (I think) bolt and remove the speedo drive. Check to ensure the drive gear is still attached. The hold light doesn't keep the speedo and cruise from working the failed speedo drive does. Easy 10 min check, can't find these new anymore so look at wrecking yard. Keep in mind that the Ford Probe is a great donor car for this.