I’ll be finishing up installing my remote trans cooler over the weekend and I’d like to trigger the fan relay with the OD switch on the shifter. Is this possible, and if so where is the best place to tap my trigger wire? @IBMobile posted a diagram a while ago showing the circuitry, wiring, and fuses between the PCM and the shifter button (switch) that command OD on/off but I don’t understand it well enough to start cutting wires yet. His diagram shows fuse #14 powers the OD on/off light, so can I tap it there? And where is fuse #14 actually located?  I’d tap into the wiring from the on/off button on the shifter, but it’s a momentary switch so I don’t think I can do that without using a special relay. 

Why not use a ISSPro EV2 gauge you program the gauge to trigger an option cooler fan. Then set the warning light for danger limit. All of ISSPro EV2 gauges have this function.

 

Like you can set a boost gauge to trigger a methanol spray kit to turn on at a set boost pressure.

 

Lots of options.

1 hour ago, Andyba20 said:

I’ll be finishing up installing my remote trans cooler over the weekend and I’d like to trigger the fan relay with the OD switch on the shifter.

 

Are you saying that when you activate the OD switch on the shift lever to shift into fourth gear that you want to turn on the transmission cooler fan?  I am not sure what your objective is here.  If this is what you are trying to do, then I don't think wiring it this way is beneficial.  Shortly after selecting fourth gear, the torque converter will lock up.  When that happens, virtually all heat that was being generated by a slipping torque converter ceases. 

 

If I am misunderstanding what you are trying accomplish, then please disregard the above.

 

- John

You can install another push button switch in the shifter and use it to trigger the relay.  I've installed one in my truck as well as @JAG1truck.   Here is how to do it.

https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation_50/52_transmission-transfer-case/diy-lockup-switch-install-into-gear-selector-arm-r384/

Use an on/off switch.  Take power from any hot, with key on, wire under the dash and install a 2-3 amp fuse in it.  Run that wire to the shifter on/off switch that you installed.  From the on/off switch run a wire to the PCM and connect it to terminal 86 of a mini relay that you can install in an empty slot.  Run a ground wire from terminal 85 to ground.  There is a blank spot in the PCM for an extra fuse.  Run a wire from the fuse to terminal 30 on the relay and a wire from terminal 87 to the fan motor.  See the article "Installing Protective Lift Pump Relay" in the fuel section , it has a lot of what your looking for.

https://mopar1973man.com/cummins/articles.html/24-valve-2nd-generation_50/51_engine/59_fuel/installing-protective-lift-pump-relay-r501/?tab=comments#comment-55

 

If your looking for the fan to come on automatically when OD is locked out, and your towing, that can be achieved, I think, with 2 relays and no switch needed unless you want one added for more control .   I'll have to draw up a diagram later to see for sure.

 

I’m wanting the fan to turn on when I tap the shifter button and lock out OD. Trying to avoid having to install another dedicated switch in the cab, I’ve got too many as it is. Also, this way I’m running the fan by default when I’m towing, or when I’m in stop/go I can just tap the shifter to turn the fan on. I’ll probably have a thermostatic switch as well, but have heard mixed reviews on their reliability so the OD off trigger option essentially gives me manual control. 
 

This was responding to @Tractorman question.

15 minutes ago, IBMobile said:

If your looking for the fan to come on automatically when OD is locked out, and your towing, that can be achieved, I think, with 2 relays and no switch needed unless you want one added for more control .   I'll have to draw up a diagram later to see for sure.

This would be more what I’m looking for, but don’t go out of your way to draw anything up, I just thought there might be a simple way to tap a trigger somewhere between  the shifter button and the PCM command to lock out OD. 

It can be done using two relays and the factory OD switch.  I drew up rough schematic on the back of an envelop while having my afternoon coffee.  If your interested I can draw up a more detailed schematic an post it.

Bolt this into a tranny test port. Cheap alternative.

https://www.amazon.com/AUTOHAUX-Universal-Automotive-Radiator-Temperature/dp/B0BKSV137N/ref=mp_s_a_1_17?crid=3IC0IY4GZQUOL&keywords=1%2F4+npt+coolant+fan+switch&qid=1682264714&sprefix=fan+switch+1%2F4%2Caps%2C413&sr=8-17

 

The iso programmable gauge would be a good like @Mopar1973Man said.