Could be low vacuum, there are three switches connected to the brake warning lamp; parking brake, pressure differential switch, and low brake booster vacuum. The low vacuum switch is activated if the vacuum falls below 8. 5 inches for more than 10 seconds. As the vacuum pump is engine driven, I would suspect this could be the problem. Hopefully it would only be a leak and not the pump giving out.
The antilock lamp is another matter, which from consulting the manual, could be for numerous reasons, you would have to retrieve the fault code to be able to identify the problem, but however fault #11 has to do with the brake pedal swith, and if you are having a vacuum problem, the pedal may be droping slightly and tripping the switch. To clear the fault from the antilock control module just disconnect the battery or alternately unplug the module for 30 seconds.
Hope this will help you, if you wish to retrieve the fault codes email me at the link bellow.
Neil
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Neil Copeman 92 D250,LE,limited slip, 16cm turbo housing, Isspro gauges, factory tach option, Lear cap, DC crankdown tire carrier
Hadley air horns, Stealhorse leather seats, e-mail (home):
bombedcummins@sympatico. ca