Some things you can do - if applicable

Check condition of wires to sensors - the wire to the right front of our '90 744 TI was worn half way through by its wide tires - I was able to reposition it in its holder to avoid further trouble.

Check grounds around and for the ABS unit

Examine and clean tone rings and sensors.

Check and clean all connectors - my '90 744 TI had some under the hood, under the dash, and in the trunk.

I never really found my problem, but I did get the ABS to work upon every startup and the light only came on about once every 5 trips or so - often when hitting a certain type of bump. It did work properly one snowy day when I REALLY needed it!
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '72 Yamaha Rd400, '68 Honda 350-4, '12 XC70, the first 5 are mine, heh, heh, 525,000 miles put on 10 bricks James A Sousa