Also make sure the Alt is putting out full voltage, below 11.4 the ABS will signal a fault as it isn't getting enought volts to operate in default mode.

Bentley manual has a very detailed trouble shooting procedure. I'd suggest that you get the manual, a multimeter, and do all the checks.

In my case, I found two faults on my 'new' '93 when I found the ABS non-op.

1) A blown fuse on the surge protector. Oddly enough for a regular fuse, it is located underneath the passenger seat, you need to unbolt the seat and pull the carpet back to get to it. No clue if this is the 'usual' reason ABS will go off line or not.

2) Second fault indicated by the procedures was that the ABS warning lamp had been removed. Naughty previous owner!

The only other thing you might do before getting the manual and doing the whole procedure is to check the front wheel sensors. They are magnetic, and over time the tips of them can get covered with rusty bits of metal, this can cloud the sensors reading of the tone ring on the hub. Remove, clean, replace. They don't need to be squeeky clean, just no wooly willy hairdo.

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'63 PV544 rat rod, '93 Classic 245 + turbo