Controlling the locking converter

Submitted by: "Louis A. Mendes" (lmendes at

OK Guys and Gals, here's the promised circuits for the TCC Lock and Release
Circuits, with lights...

The explanations may seem long to some, but I would like everyone to be able
to understand what is happening at each phase, so please bear with me...

Firstly, in order to properly fill in the gaps on the TCC circuit, there are
two separate portions to the control of the TCC...

        (a)     Part 1 -- the ECM controlled portion that locks the TCC
                                *Normally open until the ECM closes it.

        (b)     Part 2 -- the ECM controlled portion that works in
conjunction with the                                      brake pedal,
cruise control, and engine vacuum functions to
                                disengage the TCC.  *Normally closed until
opened by the
                                brake pedal.

As such, there must be two separate switches; one for each portion of the
control from the ECM to the TCC locking solenoid and unlocking circuit.

PART 1 ---

Frank S.'s original thread and George D.'s repeat of such thread about the
TCC Lock circuit is 100% correct; the ECM would normally ground the TCC
Solenoid at a given speed (controlled by the ECM) to lock the TCC...

By bypassing the ECM to TCC Solenoid circuit with a simple SPST switch
between pin 'F' on the Assembly Line Data Link (ALDL) connector and 'Ground'
tricks the TCC solenoid into locking at an earlier stage...

To verify the correct wire, in case the terminal connection cannot be
identified, then look for a TAN wire with a WHITE stripe within the ALDL
wire harness...

 Tan/White Wire ------->[switch ]       [switch ]----------->to ground
                                 [end #1]       [end #2]

When the switch is OPEN, the circuit will function under NORMAL ECM
controlled function; when the switch is CLOSED, the TCC is ENABLED.

If you want to add a light to tell you when the TCC is Locked, the simplest
manner to connect a load circuitis as follows...

 Tan/White Wire ----->[switch ]   [switch ]-----------> to ground
                               [end #1]   [end #2]
                               [SPST  ] ------------->[12V lamp]----->to +12 V  

In this way, when then TCC Locks, the entire circuit will "clamp" to Ground,
thus completing the connection through lamp circuit.  Until the TCC locks,
the lamp will not be lighted.

PART 2 ---

As Don Bryer, brought up in his thread up a possible DISABLE function, he
was right in that the lead from the back of the brake pedal would work in
disengaging the TCC from locking.

This is the reason that by pressing down on the brake pedal disengages the
cruise control function, and also starts a 20 second delay that unlocks the
TCC solenoid in the process...

In order to keep the TCC unlocked (for towing, etc. as mentioned in Don's
thread), your would connect a simple SPST switch on the PURPLE lead that
exits the switch on the back of the brake pedal... this lead is the ECM
Breaking Switch...

So, the switch could be setup as follows:

       Purple Wire ------->[switch ]       [switch ]----------->Purple Wire
                                 [end #1]       [end #2]

This switch tricks the ECM into thinking that the Brake pedal has been
pushed down, thus disengaging the TCC in locked mode, or from going into
locked mode.

So, when the switch is OPEN, the TCC will unlock; when it is closed, it is
under NORMAL conditions.

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