Steve: Assuming your 400 has an Onan engine in it, I would have you're existing starter rebuilt. I recently had both of my 318 starters rebuilt. One was $53 and the other was $83. I don't know why one was $30 cheaper than the other and didn't ask as they were rebuilt about a week apart. They replaced the solenoids, turned the armatures, installed new brushes and bushings and cleaned them up. Both starters work like brand new. The cheap aftermarket starters are made in China and from what I have heard are low quality. I broke open one of the old solenoids and the problem was the solenoid - the copper contact strap and copper bolts were arced and could not make good contact. That may be all that is wrong with yours. If you have 12 volts available at the solenoid and if you jump across the large copper bolts and the starter cranks, then your problem is the solenoid. Just be sure you get a quality replacement solenoid.