I assume the 37 amps is free spinning at the large post?

The amperage you are interested in, however, is the small solenoid post, not the large post. Remove this wire and test the resistance to ground at the wire. It should be infinite. Then see how much amperage is used to activate the solenoid through the small post on the solenoid. It must be below 20 amps.

You may have a second relay between the switch and starter that could be shorted.