Second Battery for P38A
Second Battery
I added a second battery to my Rangie so I can power some accessories without the engine running. My truck is a 2000 NAS model, so I have the extra power outlet back in the load space.
The aux outlet in the back normally turns off when the key is off, exactly like the cigarette lighter up front. This has become annoying for the kids watching a DVD in the back seat; every time we shut off the truck, the DVD forgets everything, and they have to sit through all that stuff on the beginning of the disc that you can't skip.
There are a couple ways to connect an auxiliary battery. If you want to also provide power to the front lighter and the truck radio, follow the VERSION #1 instructions below. If you only want to power the rear aux power socket in the load space, follow the VERSION #2 instructions.
Regardless of which version you use, the second battery is connected to the +12V of the vehicle to charge whenever the key is ON.
For either version, I installed the battery in the spare tire space. Cutting away some of the styrofoam that holds the factory jack makes a perfect space for this battery. A short piece of nylon tie-down strap keeps things nice and secure.
Considering my application, I didn't go for an Optima battery; I didn't need that kind of capacity. I used a motorcycle battery instead; its fairly small, and provides all the power I need. This will provide enough power to watch a DVD when we're camping (not exactly roughing it, are we?) without affecting the main truck battery at all.
VERSION #1
I routed the wires from the battery under the carpet toward the CD changer. Removing the trim panel from the left rear of the load space also reveals an access hatch for the left rear light cluster. Just inside this panel is where the battery will connect to the vehicle wiring.
A quick look in the ETM reveals both switched and unswitched power in the left rear access area. Could this possibly be more convenient?
Connector C1358 is the one we're looking for. If you don't have trailer wiring installed, the connector will "dead-end" in this access hole. Disconnect C1358 from the plastic clip and pull it out so you can see it.
Pin 1 has a BLACK wire on it; this is GROUND.
Pin 4 is WHITE / ORANGE; this wire is +12v when the key is ON. Pin 3 has a PINK / ORANGE wire that is always +12v.
Using a couple of everyone's favorite 3M Scotchlok (suitcase) connectors, splice the new battery (-) to the BLACK wire. Splice the new battery (+) to the WHITE / ORANGE wire. The new battery is now connected to the load side of fuse F8, which supplies the lighter socket(s), radio, navigation & HEVAC ECU.
C1358 is pulled out of the access panel, showing the ScotchLok connectors
Remember that since the radio is now "always powered", you must turn it off when you get out of the truck; the radio will no longer go off when you turn off the key. Failure to turn off the radio will discharge your second battery.
VERSION #2
I routed the wires from the battery around the spare tire well and under the carpet, toward the right rear lamp cluster access panel. In the 2000 (and up?) models, the auxiliary power connector is here. Looking inside this access space, we easily see the back of the aux power connector. Remove the 2-wire plug (C0350) on the back of the power jack for easier access to the wires.
Reach down inside this panel to access the back of the aux power outlet.
The BLACK wire is the GROUND connection. Splice the new battery negative (-) to this wire using a ScotchLok connector.
The other wire is GREEN. This wire is +12V from the truck battery when the key is ON. This wire must be cut. Leave enough wire before the connector so you can tap into it with another ScotchLok connector. Connect the new battery positive (+) to the connector side of this wire.
This is the 2-wire connector on the back of the aux power socket
Connect a 10 amp diode to the wire coming from the front of the truck. Polarity is important here, the STRIPE on the diode should be closer to the aux power outlet.You can use the ScotchLok connectors with the diode, or solder it into the connection.
This diode must be able to pass the full charge current to the second battery. You may be able to use a different size depending on your current requirements.
These are the wiring changes you need to make.

This method connects the second battery only to the aux power connector, the diode does not allow current to flow toward the front of the truck.
The diode does allow current to flow from the +12V feed from the vehicle when the engine is running to provide a charge to the secondary battery.
If you use the diode as described here, note that the voltage passing through the diode will be approximately 1 volt LESS than the voltage going to the diode. This voltage drop is normal.
If you make either of these changes, you should print the appropriate pages of the ETM and mark the updates before inserting the new pages in your book.
Several of the images above (P5622, P5607, P6191, page J1-1) are from the Land Rover RAVE disk #3, 2000MY Electrical Troubleshooting Manual.
Those images are the property of Land Rover.
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