ABS Light/Emergency Brake Light

Hello All,
I'm a new member and have learned a lot from just reading the posts.
I haven't run across my prob. yet. I have a '98 Silverado 5.7 eng.
231,000 miles. Truck runs like sitting in showroom, but recently when I
turn the fan on (A/C vent heat ect.), the instant I turn the switch,
the ABS light comes on and the fan w'ont blow. Turn switch off, then ABS light flickers and alternates w/emerg. brake light. After about 20 seconds both lights will go out. Sometimes the fan will now work, sometimes not. When ABS light STAYS off the fan works
Any ideas??
Thanks in advance,
Danny

I don't have an answer for your problem, but I would like to comment on your vehicle. Have you owned the vehicle from new, and, if so, where have you driven it to accumulate 231k in 7 years. I'm at 176k on a 1991 Century, but didn't think there were those out there with that much more. Thanks, FastNBody2002

Fast,
Yes, truck had three(3) miles on it when I bought it in '98.
Drove back and forth between Dallas, Tx. & Southwest MS
just about every weekend.(1,000+ miles one way) Only thing done to it has been replace alternator, Battery, water pump, brakes and intake gasket. It runs like a dream except for ABS light prob.
Wife just got home from town and milage is 231,134.7