Spedometer stopped working

I have a 91 Accord. The speedometer started going wild, 30 mph. 75 mph and I was at a stop finally quit working and the S light came on. I finally changed the speedo sensor and the S light went off...Check engine light was also on, read on a forum that the speedo sensor does more than control your speedometer, maybe that your trans is not getting the info it needs to shift.....

If it's running rough, chances are that it's misfiring. If the Check Engine light is flashing/blinking, it is definitely misfiring.
If that's the case, drive it as little as possible... Or straight to the mechanic because the more you drive it while it's misfiring, the higher the chance is of you ruining your catalytic converter.

I’m happy to help further over the phone at https://www.6ya.com/expert/jason_00b31cc8f593773a

You need to replace the vehicle speed sensor located on the trasmission.

In cases where both are not working, i believe that it might point to a faulty speed sensor. Is your check engine light on? If so can you retireve the code from it. If not, manualy check the speed sensor. If you need to know how to do this, please let me know. Please rate my response for me. Thank you

Your instrument is bad, The spiral coil for the needle is alraedy out ot calibration therefore it has been jumping around. Even they reset, it already been stretching. It needs a new one.
Don't waste mony for the reset.
It is probebly expensive from dealer plus labor. Just to check out the price,
You can get a used one from ebay for $85. However, you need to know how to replace it. Let me know it you need any help.
Meanwhile you can gauge your RPM to keep your speed under control on the long trip.For example: 2000 rpm is about 55 mph. Try to keep it below 3000 rpm so you don't get over speed limit.

HI, the speed sensor is damaged. replacing the sensor will fix this issue.

If all the connection and power supplies to instrument cluster are ok,I suspect that the speedometer or instrument cluster is faulty but before you replace it, make sure the gear inside the transmission that drives the VSS is in good.

check the ground wire for thi lite as it sounds like it is dirty or making bad contact.

A green flashing "S" is similar to a check engine light. It is telling you that something in or on your transmission is not functioning correctly, such as the speed sensor or shift control solenoids. If it starts flashing and the speedometer stops working or the transmission shifts weird, take it to a mechanic.

Replace them.