I changed my alternator from an external regulator to an internal regulator, and now the engine runs on for about a minute after I turn the key off. it did not do this before I changed alternators
Truck is a 38 gmc with new drive train and Rebel wiring kit, I wired the alter. exactly the way rebel said to. so whats going on that it keeps running on after the key is turned off. I know it is some thing simple

thanks

1938 Gmc 1/2 ton