Brake failure 328 w/ABS

Had brake failure light come on then few minutes later rock hard pedal with maybe 10% braking ability. I have a 1989 328 GTS with ABS. Eric, an awesome Ferrari mechanic from The Auto Gallery in Calif was on the Ferrari group run and made it so I could limp home. He pulled relay 38 or 37 of the ABS system, the green one, and connected a wire to the contacts and made it so that I could energize the ABS pump every time the light would come on. So after maybe 5 or 6 brake pedal pushes, the brake failure light would come on, then I would close the pump circuit wire from the drivers seat and after 15 seconds the light would go out and brakes would be fine. So not sure what as failed. Pump works, ABS failure sensor works since the light comes on and off. Swapping out relays didn't help(have friend with Mondial and exact same relays). Are there other sensors to try? I feel bad not taking it to the mechanic who helped me, but I cant afford it right now or afford to trailer the car 50+ miles to his dealership. Thanks.