Thanks for catching the non-computer function of the 700R4, Treblig. The lock-up function adds weight to the reciprocating assembly too, so for a drag only car, a guy might want to consider that.
I use a normally open switch in the 4th gear circuit along with a simple toggle switch wired with 12 Volts to engage or dis-engage the lock-up feature. This way it only will lock in 4th gear.
It is very much like having a 5th gear, as even with a highly efficient, high-stall 3600 rpm torque converter, there is still about 350 rpm drop when cruising at freeway speeds.
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