A hobb switch is just activated by pressure in a line as opposed to your foot or finger, there is a port on the transmission for line pressure, the pressure off the port is about 1psi for every 1 mph so you could set the switch for the speed you want lock-up or overdrive to engage

 

Great idea. working on my 94 w/47rh. Have the t/c lockup spliced into plug behind air cleaner now. previous owner has potentiometer in place of tps. Not liking that. want to eliminate that and install O/D and T/C on separate switches with indicator lights so i know they are engaged. sound do-able? I think you may have this set-up?Do you have a wiring diagram.Thanks

 

Just got my 1998 12 valve truck! It's been years wanting to learn and understand and have a diesel! However the truck I got has got several Mods...
One is this use of a toggle switch. From what I can tell it's for the TC? It to me seems to be wired wrong, but unsure. It had a wire shoved behind a fuse that went to the light diode(very thin wire) then it came out of the diode to the tog switch(even thinner wire) then the tog had a ground going to the dash metal and the other wire went out the firewall...all the way to pass side to the Computer-ECM-PCM...I'm not sure I like any of it! I'm more interested in a proper way this should be done. Are there any great educational threads with pictures or videos for me to learn? I'm a bit worried that other things may have been Mod...so how can I tell and will that prevent me from putting a better set up in than this tog switch thing... Newbie patience ....with me...thanks!