Mikey:
The TKO 600 electric speedo sensor we sell (part#LC 12222) is for "GM" TKO 600. Do you have a "Ford" TKO 600?? If so, that is probably the issue. We only sell Chevy/GM TKO's
We have sold dozens of those electric speedo sensor for GM TKO 500 or 600 with out any issues.
Hope this helps,
Thanks, Scott Lindquist
Classic Chevy 5-Speed
www.ClassicChevy5Speed.com