I don't think you HAVE to connect battery negatives imo seems like a lot of money for wiring you don't really need. Grounding to your chassis in the rear should be just as good.(Do you send you amps ground back to the front battery? No) As for an Isolator a lot of people told me you don't really needed, but you CAN use it if you want it will slightly increase the life of both your batteries(Assuming they are different if they are the same Wear/Brand/Specs then isolator won't make any difference unless you want it so it doesn't drain your starter while engine is off) To reduce dimming Increase Alt to Battery, Battery to chassis, Engine to Chassis. I just did Engine to Chassis today and noticed a slight reduce in the drop-age in my Voltage meter. Tomorrow I think I shall Do the other 2 and see how much better it gets.