While one still at the mercy of the alternator's voltage regulator, as to how many amps could flow, I recommend one go fat on the cabling and oversized on the Solenoid.
I've read that when the solenoids fail, they fail with the contacts seized together, meaning NO isolation with engine off, and a deep cycled starting battery along with the house.
Also ideally, the solenoid trigger circuit would only become live after the engine is actually running, not with the Key to ON. An illuminated toggle switch would be employed if I could not find such a circuit to act as the trigger.
I would not want my house batteries contributing to starter motor current. This also beats up the solenoid contacts more.
Cole-Hersee-24213
200 amp continuous
Silver Tungsten carbide contacts.Step up to 4awg minimum.
Be aware that some solenoids are latching, and should not be fed a continuous 12v, just a momentary 12v pulse to latch or unlatch.
I was unaware of this one one vehicle I was trying to troubleshoot, and apparently so was the person who tried to install it originally.
