Bouncing ammeter

You can solve it.
The ammeter is in the battery output/charge wire.
Full right points to 40 amps Charge. (it could be more than 40 amps but thats the max the meter shows)
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There should be nothing attached between the battery positive and the ammeter.
But if you have attached anything the draws power in between or at the ammeter or the battery positive terminal, then check those additions.
Also be sure the starter cable isn't shorting to ground.