Dual Battery System for ’91-’97 Land Cruisers •  by: Christo Slee

Click on the picture above to get a PDF document of the schematic

Adding a winch, auxiliary lighting or an other power hungry accessories might put too much strain on your stock battery and a need for a seconds battery soon arises. In addition to reserve capacity, a second battery is an excellent way to ensure that you can get out of the boonies when your main battery fails, or is killed by winching or leaving the stereo on for too long.

After contemplating different systems and our own considerations we came up with the following list of requirements:

  • Charge both batteries when the car is running but disconnect the batteries when not.
  • Override the default connection behavior from inside the truck.
  • Winch should draw power from either battery or both.
  • Winch power should be disabled when not in use.
  • Self jump self mode in case main battery goes dead

Above is a picture of the completed installation

The system we decided upon consist of the following:

200 Amp Continuous duty solenoid that keeps both batteries connected when engine is running. The solenoid is activated from the charge circuit of the alternator.

Another view of the solenoid mounted on the inside fender just behind the second battery tray.

After relocating the washer bottle and installing the battery tray, the solenoid was installed on the fender, between the air filter housing and battery tray.

The solenoid is activated from the charge circuit of the alternator. The circuit can be turned off via a dash switch, thus overriding the default connection of the batteries when the vehicle is running.

The ground side circuit of the solenoid is run through a normally closed relay. This activation side of this relay is powered from the output side of the marine battery switch. A small circuit was installed from the output side of the marine switch to trip a normally closed relay on the ground side of the solenoid. This effectively takes the solenoid out of the circuit when the winch is activated.

Marine switch has inputs for both batteries and sends output to winch.

After this, the marine battery switch was installed on ‘legs’ welded to the windshield washer relocate kit bracket. 1 ga welding cables were run from each battery to the switch. Then the solenoid was connected in parallel to the switch.

The switch has the following settings:

1 – Power to the winch is supplied from main battery

2 – Power to the winch is supplied from second battery

BOTH – Power is supplied to winch from both batteries. The BOTH position of the switch also serves as a SELF JUMP START position.

Switch panel showing interior winch controls and auxiliary light switches.

Since we added interior winch controls using the stock a stock antenna switch, it was decided to add a warning light to indicate when the winch was “live”.

Air filter clogged symbol on dash that now functions as a winch warning light.We had to completely strip the dash and then we tapped into the ‘ AIR FILTER CLOGGED’ light. This light will come on as soon as the marine switch is turned to give power to the winch. The symbol is available on US models. however the light bulb is not installed. We installed the bulb and grounded the one side via a relay to get it to light up.

Close-up of military style battery terminals.