my 1990 cherokee will not shift unless i unplug the box under passenger side of dah then i can shift manually please help!!!!!!!! i also tried another box on it and it did the same thing

 

if it shifts with the control box unplugged,means the box is bad,box being the TCU(transmision control unit)

 

first Hi!; that "box" controls the way the trany will shift by sending signals to the solenoids inside the transmision. If you unplugged the "box" and u can drive by shifting manually without problems then u may have a bad "box" or one or more faulty solenoids, and if u try another "box" and it keeps doing the same it can be the solenoids.

 

i had the same problem with my 1990 4dr, replace the throttle position sensor. its the problem 99% of the time and they only cost around 30 bucks new or 10 at the jy.

 

yea I have a similar problem with my 90, Except i dont touch the box but if i dont shift manually The transmission shifts way to early, been a while since I've driven her but I believe she shifts to early like 1st, 2nd,.. nearly instantaneously and then in top gear at about 35 mph. I dont know if there similar. I havent discovered why mine does it but could be similar.