100 series batterys

I would think the second battery, not the crank. That way you can link those two together and run flat with all your appliances and still start the truck. Also then your crank batt will still charge first then the other two together. If you linked it to the crank and then forgot to isolate and ran flat you wouldn't be able to start But I am only guessing as I have never done this.

Toohey,

I think the 100 series uses two batteries connected in parallel for cranking the engine. If this is the case connecting to either is in fact connecting to both and is fine. Not sure what you mean by a manual isolator - suggest something like this one would do the job automatically and reliably. I assume you are using the third battery for household chores like running a fridge. ( Due to losses in the long cable, it won't be much help to the main batteries if you are planning on it supplementing them.)

Cheers

John

Hi Toohey,
I have installed a 3rd battery in the engine bay of my 100 series, this is connected to the 2 paralleled start batteries via a Redarc solenoid, and then run cables to fridge plugs etc to the rear of the vehicle. This system works well and the isolator will separate the batteries when the voltage of either battery falls below the isolator's set point. Another advantage is the solenoid has an external start button which enables you to start the vehicle if the start batteries fail.
Hope this info helps
Cheers
Howard

toohey,

I run a 100AH AGM battery in the rear to power accessories such as the fridge.
It is connected to the main battery through a Piranha isolator.
Has worked well for many years although currently trying to isolate a .5 amp current drain when everything is turned off.

Toohey it is true the 100 series uses two batteries connected in parallel for cranking the engine, they are 450CCA each. I ran a third battery for a few years but found the smaller size that fitted in the space under the hood did not offer enough amp hours for my application.
I split the 2 originals with a redarc, replaced the starter with a 760CCA N77 and in the other position (drivers side) fitted a 105 AH N77 as the auxiliary, a simple solution, now after 4 years I have just replaced it with a 120AH Fullriver

Hi all, i also installed the third battery under the bonnet like howard. i rerouted the wiring so both crankers are on the passenger side, the new battery carrier will only take a ns 50 size battery. i run a 710 cca and a 530 cca as crankers and a n70zz size deep cycle on the drivers side chargered via a rotronics for the auxillary. i also installed a manaul link using a master switch to link all batterys together when not running anything on the aux battery for long periods of time to make all batterys active in the system. This has increased the life of my aux battery by heaps. Have been doing the charging system on my landcruisers for many years this way and it works well. cheers mm.