The negative terminal where I'm assuming the monitor lives (small rectangular device with a 2-pin connector) was very corroded. I removed the battery again to check and apparently I did not tighten the connection completely. Removed the battery and negative cable. Cleaned the connection on the cable with one of the christmas tree style wire

Car battery charging – step-by-step. Disconnect the connecting cables. Important: The cable which is connected to the negative terminal must be disconnected first. This prevents a short circuit between the positive terminal and ground. Then disconnect the red cable which is connected to the positive terminal. Check the state of the battery.

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ford c max battery negative terminal