Thanks for the indepth reply very handy book! I must get one... I actually have a 92 ford X 4X4. I jacked it the rear whells up and yhe trans works until you apply brakes then it dies....I changed the vacuum modulator with a used one off of the used tranny I bought(60000 miles). I might invest in a new modulator after I check it to see if any fluid is in the line. Also(If I created a little mess when changing--Fluid came pouring out of the modulator hole, Quick get a bucket')but no change when i replaced. Next the brake booster grommet was leaking changed that and some vacuum lines, no change. I have read about a brake switch that can cause this problem and that is my next check. I have a snapon scanner that I will hookup next. Then onto your fix.
Thanks again for your help and will keep you guys updated...