I believe we simply ground the solenoid field and then the solenoid closes the valve which then causes the lockup valve to move over. We call that ballistic converter apply as opposed to modulated converter apply.

We did that for everything in the old days.

In the old days - all electrically controlled lockup units - made no difference what model year or trans. That all changed when we went to 41TE (604). Many people are confused what electronics do on the old units, I think because we use different names like PTU (part throttle unlock) etc. The bottom line is we turn the lockup solenoid on or off to control lockup - but all it is at the end of the day - a solenoid opening or closing which makes the lockup valve or solenoid switch valve move. The valve has to move to get or shut off lockup. If the valve is stuck off - actuating the solenoid will accomplish nothing. OBDII will set the check engine light because the controls do not see engine speed reduction after the solenoid is activated.

The only duty cycle solenoids on Mopar transmissions that I am aware of now is the 41TE (604 family), RFE Family, 62TE, NAG1 and now the 8 and 9 speeds. For both lockup and shift control. As for using a PWM to control lockup, the converter and valve body were designed for an on/off solenoid. Again, the converter does not get "turned on" until that lockup valve moves over. A PWM solenoid will accomplish nothing to smooth the converter engagement as that valve moves very little to achieve L/U. plus the damper assembly within the converter was designed to cushion the lockup apply. By dragging the lockup disc too long you put more heat in to the disc. It wasn't designed to be slipped for cushioning.