While the location I have chosen for my sending unit is arguably correct/incorrect I still feel as if I am getting an accurate temperature reading. In the end it is entirely how much work you want the installation to be, and if you want to really mess around with your hard lines or just stick in in your test port. The gauge I used was an Autometer Z-Series (electric short sweep) that came with the correct sender thread size and resistance. I placed mine knee-knocker style underneath the heater control unit rather than putting it into the cluster. Good luck.
