Hot wire when cranking engine only?

[Fallon 40]

I’m just about finished installing my second battery and need to find a wire that is only positive when cranking the engine.

The instructions say to connect to the terminal or wire running from the start key switch to the starter solenoid using a two amp fuse. The connection can be made at the start key switch or at the starter solenoid, but must be to the line that is positive only when cranking the engine.

Does anybody know where I would find that wire?
Thanks
Ken

 

[nakman]

Curious what instructions.. is this one of the dual battery kits? (IBS, Nat Luna, etc.) never heard of this before. (not that that means a whole lot!)

 

[Fallon 40]

Blue Sea #7622 automatic charging relay.

 

[AimCOtaco]

It's the small wire attached to the starter. You may be able to trace it without actually having access to the starter though (I hope). There may also be a load relief relay that would have it as it's signal but not sure if we have a load relief circuit (this is the relay that turns off the HVAC blower, electric defrosters, etc when cranking to keep max power available for the starter).