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I installed a digital voltmeter for my secondary battery. However, it is backlit and I don't want it lit up all the time while parked. So what I did was run the hot through my s-pod so that, using a relay, I can turn the meter on and off from inside using a contura switch. However, this means I now have to switch it on everytime I get in the vehicle, and switch it off when I leave. The problem is that there is only 2 wires coming out of it (a hot and ground), so the backlight is also drawing power from the battery that it is measuring.

What I'd like to do is have the meter turn on when the key is on (like the 12V acc power plug). I'm a bit of a newb at this and just can't wrap my head around how to make this work. If it were connected to the main battery it's easy, just wire it to the power plug, but I suppose I want the meter to light up from the main battery circuit, yet measure the voltage from the secondary.

Is it possible to do what I want? :confused:
 

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All things are possible, it's just the degree of difficulty that is in question. Simple fix for automatic control of your meter is to control the relay you have it wired to from an accessory circuit. Meaning that instead of running the control wire for the relay through a switch just connect it to the + wire on the 12v accessory plug in the switch panel. This assumes that the S-Pod wiring is switching the + side of the relays. Their web site doesn't have schematics so it's possible that they switch the ground side but that should be very clear in the instructions that came with the S-Pod. The more difficult part of your request is making the backlight operate separately from the meter. This will require surgery on the meter. The difficulty can vary from a slam dunk to call Bellydoc and schedule an operating room. You have to open up the meter to see how the backlight is connected and what it actually is. To have the backlight run from the main battery it has to be disconnected from the meter and wired independently. Do this wrong and you could be putting a fusible link between the 2 batteries. The back light can be anything from a simple 12v bulb to a surface mounted LED with many variations in between. Each of the different lamp conditions would require specific instructions that match the type of light present. I'd recommend just rewiring the control relay unless you want to get adventurous.
 

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use a relay with power source from 2nd battery and other side connected to the meter. Use an ignition switched source as power to switch on the relay.
 
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