Hi Dave,
At first glance 180 milliamps doesn't sound like a whole lot of current drain, but that represents sucking 4.3 amps per 24 hours, which would completely kill a 100 amphour battery in something like 23 days..... ruff calculations here
Not wanting to pull figures from my head, I took my trusty Fluke multimeter and took a look at the standby current drain on my brides 98 Jeep Grand Cherokee...... just .015 amps or 15 milliamps or about a tenth of what your reading.
If you can determine the source of this drain (or the bulk of it) perhaps a quick and dirty fix would be to isolate this circuit with a relay and control it with the ignition switch. If there is no electronic brain that needs a source of power to keep its memory alive, this might be the easy way to go, rather than attempt to sort out the "correct" (by the manufactures standards) way to power it up.
Good luck....... this ABS project must be a labor of love....... I love a challenge too, but this would have me going bonkers in nothing flat. Take care
- Jim -