OEM tailgate lock, supposed to see the heat shield of the harness?

You could try connecting 12V in either direction to the lock and see if in opens/closes based on polarity. Or measure the voltage on the lines at the fuse insert points. Personally I wouldn't inject exogenous voltage into the cab side of the circuit. I have no idea what would happen, but am certainly curious.

Also if there is a fuse on both wires, it would be cheap to use two add-a-fuse devices to patch the above circuit into the signal path. This would avoid the cost/searching to get a couple of the correct connectors. Of course you could just cut the wires to insert the circuit, but I have a policy on my 3rd gen to only make reversible changes to any wires based on its complexity and warranty considerations.

 

The fuses for the tailgate are there to protect (continue use) when rear ended. Failed solenoid at crash, fuses do their job. Circuit to unlock doors "should" continue normal.


5 pin relay rest on ground. Unlock to Driver's has priority unless modified in head unit or at dealership to all doors unlock at first FOB press. Lock relay is for all solenoids.

 

I now understand what you were wishing to do with the bridge.

OK, the perceived problem is not a problem at all. Thats good, but I was looking into doing something more with the vehicle to increase the security. Sometimes playing around is fun. Not at all necessary in this case, the Toyota engineers did their job well.

Turns out each door lock motor in the unenergized condition has both leads connected to Ground via the three door lock/unlock relays. Thus, any power introduced upon either of the motor wires from the rear of the vehicle would short to ground burning up wires or the relays embedded in the under-dash junction box. This would have no effect upon the door lock motors.

It's good to know why the two tailgate lock fuses are there - the wires being shorted either to themselves or ground as a result of an accident. However, after an accident it would take the activation of either the door lock or door unlock command to blow a fuse, only the second attempt at locking or unlocking would resume proper operation for the cab door locks after the circuit was opened up by the blown fuse. A shorting of either or both of the tailgate lock wires to +12VDC would result in an immediate blowing of the 7.5A fuse(s).

It took printing out the pages of the door lock schematic, cutting and taping the pages together to get the complete picture.