ford f-800 truck

I have a 1995 ford f-800 truck sva00557 cummings 6cyl. Okay guys I haven't had any luck anywhere in Al. I've searched most all the truck dealers for help on this issue. I have a problem with the electric brake motor. Everytime I leave out with the truck about 20 minutes into my route the electric brake motor sensor starts beeping and will come on and off at different intervals. I have replaced the electric brake motor the flasher type sensor, two other sensors that the dealer said may be linked to the electric brake motor one on the master cyl and the other on the brake booster. All the fluids are at proper level and not leaking. I have checked to make sure all the leads are tight and grounds are not loose. I know this sounds odd and may not have anything at all to do with this but the other guys in the truck say they can hear the truck horn beep lightly usually twice rarely when the sensor is activiated is this tyed in with the sensor? or maybe thats another problem? Anyway when I stop the truck and the sensor is still beeping I have to raise the hood and tap the flasher looking sensor on the side and it will cut off. Like I said I have replaced that sensor plus all the others but that one at least 3 times and the same problem occurs. Any help would be greatly appreciated!