I have a 79 Johnson Stinger 75 horsepower lower end model#75ELR79R SN:J5122868. I replaced the powerhead with a 77 Johnson 70 horsepower Stinger model# 70EL77S, I have to look at the 70 horse again to get the serial number. It won't shutoff. I realize that there is a kill switch wire (yellow and...