I have a 1995 Honda Odyssey with 190,000 miles. When I turn on the a/c after about 10 minutes the drive light blinks and the speedometer stops working and the odometer stop working also. So I have been unhooking the battery and it resets everything and the light works as well as the speedometer and odometer. I have about 2,000 miles on a new cylinder head and timing belt water pump, and battery and cables, wich was quite expenssive and im wondering if its worth even fixing but there is absolutley no rust and I love the vehicle 28 mpg mini van can’t beat that 
I was hoping maybe someone might have an answer? Thanks
In a Honda, a blinking D4 light is the equivalent of a check engine light for your transmission. You can hook up a code reader and retrieve the code. It could be something simple and low cost, or not.
As keith stated the D4 light is the malfunction indicator light for the Transmission Control Module. When it flashes it indicates that the TCM is finding a problem with one of its input sensors or how the transmission is responding to its output commands. As keith also stated the TCM can be scanned for transmission related codes. You may need to have a transmission technician do the scan and diagnosis.
Most likely you will find a Diagnostic Trouble Code related to the Vehicle Speed Sensor or its wiring. You probably have a problem with the Vehicle Speed Sensor. That sensor sends a signel to the speedometer/odometer head and to the TCM. Without the VSS signel the TCM will have a hard time calculating the shift points.
Hope this helps.