MIL code 12 means the Powertrain Control Module, better known as the PCM has lost power within the last 50 key cycles. Usually that means the battery has been disconnected. In your case there may have been a momentary power loss for some reason. This will not make the SE light come on.

MIL code 15 (scanner code P0500) means a fault in the Vehicle Speed Sensor has been detected. This will make the SE light come on. If you aren't having shifting, speedometer, or idle problems I suggest you reset the code by disconnecting the negative battery cable for 2-3 minutes and see if the code returns.
http://www.obd-codes.com/p0500

Do you have the 3 speed transmission?

 

Yes,I do have the 3 speed trans.I disconnected the battery and cleaned the terminals.They were dirty,I cleaned and put them back.So far I have restarted about six times and no sign of a code being set.Maybe that was the fix.

 

So far so good. Drive it around a bit to make sure.

3 speed tranny? You just confirmed for me why you got a VSS fail code and not an input or output speed sensor code. Those are used on the 4 speed tranny. I wasn't sure.

 

Well,the check engine light came back on and it is the same mil 15.This time the speedometer does not work.I was hoping someone could tell me where to find the sensor on the trans,my book does not show it.I will check the connection and the sensor.I believe the ohmmeter test is to see it shows eight on off cycles per revolution of the sensor. Thanks in advance

 

Recently saw a picture of a 3 speed tranny showing the VSS but, I'll be damned if I can find it. I want to say it's on the front of the tranny but don't recall for sure. If you don't get an answer here try posting a new thread and ask. Specify you have a 3 speed tranny. Your dealer could tell you.

The 4 speed 41TE tranny has two - an output and an input speed sensor. Your 3 speed has a single sensor called a Vehicle Speed Sensor or VSS.