The remote starter device that Jan posted bypasses the ignition switch, not the solenoid. The solenoid is a high powered relay that routes the power to the starter motor when the ignition switch is placed in the start position.
Nevertheless it would be a very helpful tool for troubleshooting your problem.
Another comment.... if you are trying to take a measurement of the voltage at the main starter power terminal while it is cranking, you might not have any luck....
It will look pretty much like a direct short to ground....