So what’s a “boost solenoid” and why do I care? This is a very helpful circuit in your coach but one that must be properly maintained and used. We will be talking about this circuit, how it works and how to modify the primary battery wiring circuit to be more understandable and reliable.
First, does your boost solenoid look like this one? 
If it does, call me immediately, you must replace it. This is a Ford starter solenoid and is not wired internally the same as our boost solenoid. What can happen? Can you say fire! 
We found this charred unit in a coach last week, the coach actually had caught fire right in our lot! Not a big one, we were right there but it could have been a bad thing. I hate to use scare tactics to get people to do things but maybe here it’s appropriate. DO NOT USE a Ford starter solenoid to replace a boost solenoid.