'87 XJ Trans Question

Just picked up an 87 XJ-auto-I6 and do not know exactly what the power switch on the dash does to the transmission. I havce people tell me that it holds the shift between gears and/or locks out overdrive. Being I still have not taken it very far yet, I don't know. Thanks for any info on the set-up.

It's changes the way the tranny shifts. In the "power" position the tranny is supposed to shift a little crisper and a little later. The switch is actually connected to the TCU (tranny control unit). The TCU controls the shift points based on this as well as input from the TPS. The switch doesn't lock out overdrive nor does it negate the lock-up feature of the torque converter.