[JL66REDCPE]

I was checking out a Cub 72 starter/generator for someone recently and some questions arose. The starter was turning over slowly using the key. When I applied 12V directly to the starter from my external battery box, it turned over fine. I next measured the voltage at the terminal coming from the solenoid and at first it read about 6V and then the voltage rose to 12V while the starter was turning. Is this a normal situation ?? I would have thought it would have read 12V right off the bat. I tried it several times with the same result. If this is not normal, I would suspect dirty wiring or a solenoid going bad - maybe. There is no amp meter or lights on this tractor. All responses are greatly appreciated.