i put in a new trans, clutch, and flywheel today. and as i was test driving it i say that my mph gague was not working and about five min later a cel came on. im just thinking its my speed sensor but i would like other opinions... thank you

 

Ahhhh...yeah. Instead of thinking about it, go out and check the sensor. If it worked before you likely just didn't plug it back in. No speedo=no speed sensor...pretty self explanatory.