I've just rebuilt the 700R4 transmission with new TCC solenoid (Type-6 system) and would like to test the TCC system on the vehicle before I reinstall the trans. It appears by the wiring diagrams I found for my 1987 S10 Blazer 4x4 2.8L w/ auto-trans that the circuit ground would be controlled by the ECM (pin A7) in opening or closing the ground for this circuit.
I figured out the circuit to test for power from the fusebox to the TCC solenoid connector through the brake (cancel) switch. I've made a simplified diagram from what I saw on larger full-page schematic.
What I need to know is when the circuit is supposed to be closed and what all other components if any have input to the ECM on this system that would control this circuit so I can test those components as well and confirm overall proper operation. I know the (+) power to the TCC solenoid is supposed to be on with the ignition key, but how and when is the ground controlled?
According to the larger diagram; The (+) power runs from the fusebox through the brake switch to a harness connector where the wire changes color from Purple to LT Green/Blk, then through a second connector where it changes back to Purple and into the "A" pin on the 700R4 transmission connector. The (-) negative Tan/Blk wire runs back from the "D" pin to the second connector where it splits back to the "A7" pin on the ECM. What makes the ECM open or close this circuit?
The diagram also shows this Tan/Blk wire continuing back through the second connector changing to Drk Blue to the first connector. It then splits back with a Tan/White wire to the "F" pin at the ALDL. It would seem I should have continuity to ground at this "F" pin only if circuit is closed by the ECM. Does this sound correct? Would this be where to test for overall system operation if/when ground is enabled by checking continuity to another ground source?
There is also a vacuum line going to the cruise control diaphragm from this brake switch. I know the brake switch plunger knob is supposed to cancel the TCC solenoid operation with pedal movement. What factor does this vacuum hose have in the system? Would this be a "low-vac" switch I've read about for custom hot-rod applications for canceling the solenoid operation when at wide open throttle or low vacuum conditions?