Schizophrenic ABS light

'92 B2200 efi rwd short cab, aftermarket wheels recently installed increasing overall wheel diameter by one inch, been driving on 'em for over a week prior to light illuminating. ABS light will come on with the brake light following suit shortly after intermittently, I might be over thinking it but brake peddle seems to vary in depression pressure as well, however fluid level is as it always has been. I've grounded out the diag plug and it gives me one flash on the ABS light after it does it's self check out twice at start up. I have no idea how to pull code from that, so any help with this issue is much appreciated as I would really like to get back to enjoying my truck.

Maybe you need to pull the ABS sensor from the top of the differential and clean it. It could be coincidental but maybe the sensor has a build up of iron filings on it and that could be causing the light to come on.

My .02.

checked the speed sensor out and checked the rear brake adjustment all was good opted to simply disconnect the abs under the drivers sear truck drives just fine now. Thanks for the suggestion