Article by: RobRed

Applicable Models: 100 Series with aftermarket head unit and amplifier system plus auxiliary battery
Last updated: December 31, 2013 at 14:53 pm

Before you begin any modification to your vehicle you should fully understand what you are doing and make sure you have the skills to complete the job. TLCFAQ nor it’s authors, commentors or contributors accept any responsibility, or liability for any mishap or problems from any materials posted on the website. Any and all of this can cause serious damage to you or your vehicle. Always consult a qualified professional. I’m Serious. Do this at your own risk.

One of the great joys in modding my Land Cruiser has been dumping the horrible factory audio system. I chose a nice Pioneer navigation head unit with a touch screen and a 5 channel digital amplifier from Arc Audio. They sound great. While I was installing my auxiliary battery system it occurred to me that even though I have power when the truck is off, the head unit is powered from the ACC circuit in the factory electrical. I want the option to power the head unit even with the key out of the truck. It would also be nice to have my HAM radio powered without the key in for monitoring or using the cross-band repeat functionality.

Problem solved. My Arc Audio 5 channel amplifier is already powered from the Aux Battery system and it gets it’s turn on signal from the head unit when it powers up. So all I need to do it power the head unit and the amplifier will turn on. One Bosch relay coming up. By wiring two power sources, ACC from the main battery and 12v+ from the Aux Battery, to the relay  (87 and 87A) it acts as a gate/switch for the power source running to the head unit. By powering the relay coil from the Aux Battery as well (#85) it’s always on and ready to be triggered. Putting a toggle switch on the line leading to the relay coil (#85). I now have the ability to toggle the head unit from normal operation via factory behavior with the key to “on and powered” via the toggle switch in-line.

[UPDATE] This has been working great as designed but one of the annoying things is the Pioneer will reboot when the truck is started (before and after this mod). I decided to fix that problem by adding an additional relay on the B+ (constant battery) circuit. This configuration allows me to trigger the toggle switch to “on” before I shut down the LC, use the radios and then start up the truck without interrupting the power – NO REBOOT. Look at the diagram below “Head Unit Relays from B+ and ACC”. While I was installing the second power relay I opted to fix another annoyance – the illumination. Basically While I’m parked key out I want the display to be in night mode so it doesn’t light up the cabin like a search light. I added a third relay to accomplish this function (see “Overall Wiring” diagram). Since I already have an illumination signal interrupt switch in the dash to override night mode on the Pioneer I have the ability to use daylight illumination with this configuration as well.

My HAM radio is already powered from my Aux Battery however I used a relay to control the unit so it shuts off when the key is turned off. By running a connection from the output of our new head unit relay to the HAM radio relay I now have the ability, with that single toggle switch, to power up the stereo and the HAM radio. The trick on the HAM radio relay is to use diodes to prevent back feeding of the power to either the main system or Aux Battery system.

The functionality is when I toggle the dash mounted power switch “on” the Pioneer head unit wakes up, triggers the audio amplifier on, puts the pioneer in night mode illumination and wakes up the HAM radio.

Below are the relay configurations as well as my overall Aux Battery layout. If you have questions or need some tech support hit me up in the TLCFAC Communications forum.

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