I have one of these:

MASTECH MS2108A 4000 COUNTS AC DC Current Clamp Meter Backlight | eBay

It is what I would use to trace down the current since it has a DC clamp on. There are lots of clamp on current meters but most can only do AC. This one can do AC and DC. With this you could follow the current to its destination.

I don't have any bright ideas where all that current is going. You might try disconnecting the alternator to eliminate that.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra