Adding a manual fan switch??

[JMBT]

Thank you all for the info. That's what I was afraid of. I sure don't need any more reasons to throw fault codes.
mmssvv, if the part number isn't too hard for you to find, I would appreciate it, but if it's a pain in the ass, no worries, i'm sure i can find something.
I have heard if I can find the corresponding pin on the Volvo OEM harness at the ECM, I can switch it through the ECM. Then enable manual fan mode with insite and get no codes, but I cannot find a pinout diagram for the Volvo OEM to Cummins ECM connector. If any of you know where to find that please let me know. If not I will end up going with the second solenoid idea.
Magard, I like that idea too.