Torque Converter Lock Up
In normal operation, the torque converter is locked up when the tan/black wire from the solenoid is grounded by the ecm. By inserting a switch between Terminal F of the ALDL connector and ground, one can manually lock up the torque converter by flipping the switch and completing the circuit to ground. Chip makers can program their chips to allow the ecm to lock the converter under w.o.t. conditions at a user selected miles per hour. For street cars, I prefer to do it manually in order to prolong the converter life. If it locks at full throttle every time, the clutches will wear more quickly and there is really no need to do so unless one is racing and striving for every tenth.
If the converter refuses to lock up under normal operation, or when forced by a manual switch, one has to determine if the problem is in the circuitry, or in the solenoid, itself.
The circuitry, as shown below, is simple and one should verify it's operation first. Power is taken from the ECM/SOL fuse. After verifying it is good, one should go straight to the switch mounted on the brake pedal lever. If the switch is properly adjusted, there should be 12 volts in the purple wire coming from the switch when the key is ON. In order for the this to happen, the switch has to be adjusted so that the button on it is fully depressed when the brake pedal is not being depressed. Sometimes the pedal will begin to be positioned a bit lower than normal and the button on the switch will not be depressed enough to complete the circuit through the switch that originates at the fuse. Sometimes one can lift up on the pedal slightly and complete the circuit so that the purple wire shows 12 volts. In this case, the tcc switch must be pressed a couple of more clicks thru its mounting bracket. If the pedal cannot be lifted, then the switch should be pressed down a couple of clicks to see if this completes the circuit. I have found that the contacts inside the switch can be burnt, but, the switch may be opened, the contacts filed clean, and the switch will work when reassembled and reinstalled.
When voltage is verified at the purple wire and the torque converter does not work, one needs to confirm continuity in the tan/black wire. As seen below, one should see continuity between A7 on the ecm and the other end under the car in the plug that goes onto the tranny connector. I often short cut the process and see if I have continuity between Terminal F on the ALDL and the plug under the car. This does not confirm the connection all the way to the ecm, however.
If one finds continuity in the tan/black wire, then the tcc solenoid in the tranny has probably died. Many have become toast after this number of years.