[Trevor]

When I design something I subscribe to the "KISS" principal, so it is pretty simple.
It uses a LM741 Op-Amp configured as a comparator, comparing a regulated set voltage to the Throttle Position Sensors voltage. When the TP voltage reaches 1.8 V the Op-Amp sets to turn on a transistor to operate a DP/DT relay.

Why not a simple transistor driven voltage sensitive DPDT relay? I gather there is a direct connection to the TPS. This means that whenever the throttle position provides 1.8 V. or more, torque reduction can not occur and line pressure runs free, regardless.

One half turns the TCUs Torque Control line off the ECU and on to a regulated 4.5V, that it can pull up and down happily.

This indicates that the torque control signal is applied to the output from a 4.5 volt regulated supply. Phil has advised that the torque control is a binary switch not a voltage. It is either On or Off. Therefore the described arrangement will ask the torque control to short circuit a voltage regulated supply, backed up by 14 volts. Interesting stuff.

The other side of the relay inserts a resistor in the A solenoids control line to limit its signal to 5%. This action keeps both the ECU/TCU from posting trouble codes.

The circuit looks like this, the Throttle pressure signal is a 12V duty cycle that is run through the dropping resistor to reduce the signal to a 5V. signal to mix with the 5V shift signal. It is therefore claimed that the shift signal to the solenoid is at 5v. The inclusion of the resistor to allow the two signals to drive the solenoid even though they may be opposite. Opposite? At negative potential? This happens when the throttle is wide open its duty cycle signal is 5%, when the shift is to operate the shift voltage is increased to about 80% to soften the engagement, if the resistor was not used one line would short out the other line, Why? They are of the same polarity. so it acts as an isolator, or voltage divider. In order to operate as a voltage divider the so called ‘throttle signal’ must be at negative potential.

Everything indicates that the resistor circuit must be at negative potential, which it is not.

When the Small Cars Shift Kit is used, the reduced resistance in the Throttle line causes a higher line pressure that (?than) would normally be used, but even with this in place, a full throttle change still has the line pressure reduced through the shift line, Exactly how? so it really does nothing but fool the driver into thinking it is producing a solid change. (Not according to those who have it. The secondary resistor included in the kit is of high resistance and is included only to prevent a fault signal. The effect equates with fully opening the circuit, which has been found to have a definite effect, confirmed by many who have tried it.)

The "Q C" may work, but not in the way intended or described and only as result of luck.