the 1987 G100 charade used a aisin built 3 speed electric shift automatic, it has its own TCU (computer) and 2 additional sensors in the car, a unique throttle position sensor and also a speed sensor in the gauge cluster.
if you simply slap the auto gear on it - it will never shift as there is no ECU - it will be forever stuck in 3rd gear - please note that it was 3 spd, final ratio is 1:1 like 4th gear in manual version.