[Andy A.]

And, just to add some more noise:

The window motors are, by design, intermittent use devices. They aren't intended to be run for more then few seconds at a time. They will of course run much longer then that, but heat will accumulate. Just running with no load (other then the transmission) will warm them up. Running with any significant load will cause them to get very warm to the touch.

Luckily, like most of the automotive sourced motors in the past, they are pretty hardy. They won't typically fry from 'normal' FIRST use. If things get overly warm, an internal thermal protection circuit will open and the motor will stop long before it's damaged.

So, whether you are running them with a relay or speed controller, be aware that some heat is to be expected.