The 4 pin ECU will work in the 4 or 5 pin wire harness. So you had a 4 pin ECU box on it and now it wont run with the other two 4 pin ECU's you have. Let me ask if this truck has the original eng and was the ECU that worked on it a factory ECU or an aftermarket ECU ? Ron

Last edited by 383man; 07/08/16 02:22 AM.