Insufficient current to drive automotive relay?
You should be looking at installing a battery splitter instead of this relay. The splitter is a pair of high current diodes mounted on a heatsink and equipped with nice stud terminals for connecting up the wires and a case cover. The alternator output goes to the common anode terminal of the splitter. The two cathode terminals connect off to each battery.

No special control wiring is required!! Also no mechanical part to wear out.







simulate this circuit &ndash; Schematic created using CircuitLab

The diodes block the leisure load from discharging the running battery. Such splitters can be found at common RV supply outlets.