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I have installed a tracker into my excavator, the tracker has power, oil pump and accessory wires.

The excavator has a negative isolation switch.

I have connected the power wires directly to the battery bypassing the isolation switch.

I have connected the accessory line to a voltage source that is +12v when the key is in position 1.

The issue is that when the isolation switch is disconnected this line becomes +12v in relation to the Acc input.

This means that the following is true.

Battery Isolator Ignition ACC Status
Off Off On
On Off Off
On On On

I believe the following accurately represents the internals of the excavator's ignition circuitry https://tinyurl.com/26hn8rrc

I need only the last statement to be true.

Battery Isolator: On | Key: On | ACC Status: On

I know I could just connect the negative power wire to the isolator and this would solve the issue, but I want the tracker to always be powered.

This question is about how to deal with a floating voltage line. I suspect needing something like an opamp or a not gate with some discrete components.

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  • On further thought over the weekend, maybe I'm overthinking this. sensing the state of the isolation switch will do, so I could use a not gate and be done. i.e. tinyurl.com/2ac4w5st
    – Mark
    Commented Jul 8 at 8:22
  • Mark - While I feel your pain (ie: your flag), if you want (or think) EE can better answer your question, frame it so there's nothing about a motor vehicle in it, otherwise they'll send it here. Give it a chance here, but I'm guessing you're overthinking the issue.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented yesterday

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