I bought an autometer gs oil temperature gauge for my truck (2004 Ford f250, 6.0) and I don't want to remove the original sender. I've heard of people doing a tee-off at the factory sender which I decided to do. If anyone has ever done this and/or knows what adapters I would need to buy at the hardware store to do a tee-off I would greatly appreciate it.

 

Not knowing the engine specs I can only suggest the following if you havent already done so seeing you wrote this over 2 months ago.
you know the thread on the gauge, is it the same as the original sender or do you know the thread? Otherwise I would gently remove it and take it all to a local hydraulic hose/fitting supplier and see what they have. Shouldnt be anything over 10 bucks and probably less.