So.... as it turns out....
The 2nd solenoid has nothing to do with charging....
I pulled the starting battery and found the nasty original wiring.... there was 1 cable that connects the starting battery to the isolator along with had 4 other wires tie off of it. The connections were bad and some of the wrapping put over the connections had disintegrated and may have been touching metal. I replaced that cable with a new 8ga cable with good ends on both.... the small wires that also ran to that were then tied to a new fuse and run to the battery connection separately.
All of the connections at the isolator were replaced including another cable from the isolator to the solenoid.
After doing this - the rig wouldn't stay running. There was a relay that someone installed aftermarket above the driver battery that I could hear keep clicking... so I started to investigate.
Turns out there was a factory 4 wire connector that someone tied this relay into (as a switched source)... they then zip tied the connector to where the other wires hang off the end of the firewall.... however there wasn't protection on the wires.... time, heat and vibration against the zip tie caused 3" or so of each wire on the connector to disintegrate, arc to one another, melting the outer sheathing.... amazed it didn't cause more problems. Cut back the harness and fixed all of that.
Turns out the rig wouldn't stay running because I missed one of the (many) connections at the starter solenoid for the battery (guessing it was the power that feeds the fuel pump / oil pressure switch system)... however had it run I wouldn't have found the other problem.
After all of the wires & connections being replaced.... both batteries charge off the alternator.
The 2nd solenoid is connected to a switch inside the vehicle that is labeled as "emergency start"... which feeds power to the starting battery from the deep cell battery when pushed. This wasn't previously working because of some of the bad connections. The reason it seemed this was part of the system is because when the solenoid is activated it then directly connects the deep cell to the starting battery....
With all of that fixed... the flashers still don't work. I haven't been able to identify where the brake switch / hazards are fed their 12V from.
