12volts is directly connected to the TC solenoid in the trans and the return wire to the pcm completes the circuit. The solenoid energizes when the pcm connects to gnd or batt neg.
So, connect a wire to gnd run it thru a switch and connect to the TC wire between the trans and pcm. This will allow the TC to be locked anytime in 3rd and OD.

 

Where is the information on this switch - as how to install - wire location/color code etc?? I could not find in the diesl section. Thanks in advance

 

I have not heard of this before either, but I can see how it could be a benefit for diesels and also gain some MPG's.

On the other hand though, while I am sure the same mod could be performed on a gasser tranny, I dont think the gassers have enough power to make this mod beneficial... but what do I know, thats just my guess. I know when my truck locks into overdrive I sure as hell better not start driving up a fairly steep grade or it will kick back out and downshift (although that may be due to 34's and 3.92 gears). Then again, thats in overdrive too... may being locked in at 3rd would get around just fine. Hmmm. Lets hear more thoughts.

 

http://www.4x4wire.com/dodge/tech/tc_lockup/

 

The gas and diesel transmissions are almost identical. One is just beefier.

The 48re has a slightly different VB strategy allowing lock up in lower gears to help with towing.

A torque converter is only at best around 80 percent efficient at converting engine torque. By locking the torque converter your making it up to 98 percent efficient. So yes you can use the TC lock up to your advantage, you would need to wire in a switch to directly control lock up.

Drag racers have been doing this for years.