I put an old cadillac engine in my 1988 gmc 1 ton.....does anyone know how to wire the stock speedo up ?The computer is completly removed.

 

Did you use the tranny that was in the truck or that came with the Caddy motor? 88 should have a cable for the speedo from the tranny.

 

the truck has the originial 400 gm trans.....the speedo wire is hooked up,but the speedo still doesn't work.

 

It is possible that the senser has gone bad, how long has it been since it worked? More than likely there is a break in the wire, try to trace it down from the tranny as far as you can to the speedo. If you cant find any breaks check your ground wires, look for any that might not have been put back on after the motor swap.