Sloan,
The fact that you can get the IP (dash) power up with the boost switch means that the system is working. The problem is that most of the boost switches are current limited and will not pass enough current to crank an engine. But, as it is working, leave it on for 10~15 minutes and then try a crank.
As others have suggested, you may have a bad chassis (engine) battery or just real bad connections in the system and that should all be investigated.
I could ask questions that would narrow the cause, but I figure if you had better information you would have included it. This is why I gave the owners that I did boat work for a meter if they did not have one. Even a cheapee would do. Before the depression, I gave away a dozen a year with my phone number on the side.
Matt