I just had the same problem. My ABS light came on a few months back but I didn't have time to look at it. Last week, the brake light came on also and the cruise control stopped working. I had the codes pulled out at the shop and it came out to 1145 and 1155 (faulty LF and RF ABS sensor). I checked the sensor for resistance and they were none (open). I replaced the two front sensors and both lights came off and cruise is now working. It seems that the cruise uses info from the ABS sensor, I guess the left one because its 20$ more expensive than the right. In all cost me under 200$ for both + bearing seals. (takes about 2 hour per side, you have to pull out the disc/hub/bearings).
I also had another code 1158 witch is dynamic RF sensor error, but that code was cleared by the shop and didn't come back (because the sensor was out). It seems like one sensor fault (1158 or 1155) could trigger the ABS light only but another (1145 or combination of 1145+1155) would trigger both ABS and brake light. The shop was a bit confused about this so I did the work myself. So get the ABS codes out from a local shop, cost me 30$.
If any of you have just a brake light issue, there is no codes so you need to check on the following things first (as I was first inquiring the red brake warning light) : Fuses ok, tail lights (and 3rd) ok, brake light switch ok, parking brake switch ok, low fluid level switch ok, low vacuum switch ok. My ford manual tells me that if I just disconnect the switch the light should turn off.
Hope this helps, this forum has helped me a lot
By the way I have a 2000 E-350, 7.3 TD, Amb. pkg now camper.