Originally Posted by Skip12
Have you checked the output of the batteries immediately after wiring them in series with a multimeter? I'm far from an expert, bit I no longer debug any electric problem without a mulitmeter. It completely removes the guess work. I start with what ever is easiest to access.
A word of caution to those who misread the bold part in this post.
You want to test with a multimeter AFTER wiring the battereis in series. Do not wire the multimeter in series. Some might see this and be inclined to wire the meter in series and try to use the Amp function. Most meters are limited to 10 amps max through the meter.
Just check for 12 Volts at the inverter input. If not there make sure it's turned on using either remote (if one is connected) or the switch on the inverter (if so equipped).
It's possible that in the earlier wiring issues that the Inverter was subjected to reverse polarity and fuses blown, worse yet, inverter damaged. If 12 volts are at the Inverter, connected with proper polarity, it's down to only switches, fuses, or the inverter itself. Check in order, power at input, switches on, and if OK to that point then the Inverter will probably need to be replaced.
FWIW, many inverters can be repaired and many areas have shops that perform this work. If time isn't critical it could be economical to repair if the inverter is a higher end unit.