Re: 81 mercury ground smoking
Your ground connections are bad. I would venture to say that thet are either loose, corroded or a combination of the two. Please do not try stsrting your motor until you get this fixed. Disconnect all the affected cables from their respective connections and check their condition. If the cable ends look good then clean them up with a wire brush or some sand paper, reconnect them and make sure they are tight. If the cable ends look damaged either by heavy corrosion, burnt/split insulation or frayed wires, then the cable ends will need to be replaced. Before replacing the cable ends, I would check the entire length of the cable/wiring for other damage. If they turned red there is a possibility of melted/missing insulation elsewhere on the cable.
This should go without saying but make sure you have the positive (red) cable on the positive battery terminal and the negative (black) cable on the negative battery terminal.
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A "shortcut" usually isn't.