i have a split charge system installed but at the mo the relay is wired so it lets the second battery charge when the engine is running is it possible to wire the relay so it only let the second battery charge when the alternator kicks in to charge the normal battery?

 

If this is on a Scoob, you already have it: the alternator "senses" when the battery needs charging.

It's just the same no matter how many batteries you have, so long as it's wired to charge when the engine is running.

Alcazar

 

i've got it connected to the head unit ign on lead atm. iv tested the 2 wires on the connector to the alternator 1 is always live the other is negative but dead when the engine is running if that makes sense to u. the car is a 2002 wrx wagon. where do i connect it to if i what it to charge automatically?