I just swapped my 79 c10 cab with an 80 c10 cab and found out thru vin it is a diesel. I am concerned about engine wiring harness. The 80 cab has 2 harneses . The main and one smaller one below the main. My 79 engine wire harness bolts on perfectly will it work? concern that it was diesel and if it will work. also concern about the smaller harness coming out of the wall and wats its purpose.